View Full Version : News on 7x46mm Murray cartridge.
While looking around for some news on the 7x46mm Murray cartridge I found this posted by Cold on 6.8 forums: ( Thank you :) )
"Cris E. Murray sent me an email, asking me to forward some info to you all. At his request, below is the info along with some interesting info about his 7x46mm UIAC!
Merry Christmas!
"I'm not a ammo guy, I'm a gun guy, I only design ammo when there isn't an cartridge to do the job I'm trying to do. The original 6.8 had a .100" free bore to accomidate a large variety of projectiles and dirt, but Remington removed the free bore section of the chamber which resulted in pressure problems. The 6.8 SPC II has free bore like the original chamber. Americans will probably see a 7x46mm UIAC PKM before they see any rifles or machine guns made for it in America or Europe. The enemy has a 18 lb. PKM and we have a 28 lb. rivet monster M240, so who's getting hosed on this deal. Feb 2010, when I get back out of Iraq, I'll be testing my first MG42 shortened and rebarreled to 7x46mm. The feed cover has been modified to run RPD links which fit the 7x46mm and there are millions of RPD links out there. I'm currently talking to S&B about making factory cases for the 7x46mm. Jan or Feb, I'll release the chamber and cartridge drawings, they are free. Thank You, Be Safe, Be Careful. Cris"
I thought many people here, just like me, may be interested in this nice "no strings attatched" cartridge.:)
Thank you Mr Murray, Merry Cristmas! and be safe. :)
Very, very nice! I've been pretty excited about this cartridge ever since Doc mentioned it a couple of years ago. It's great to see it actually get some traction and maybe......just maybe I'll be able to get something chambered in it. :D
http://i480.photobucket.com/albums/rr169/sgalbra76/762x33556x4568x43762x39762x457x4665.jpg
.30 Carbine, 5.56x45, 6.8x43, 7.62x39, 7.62x45, 7x46, 6.5x47, 7.62 NATO, .30-06
http://i480.photobucket.com/albums/rr169/sgalbra76/7x46inmags.jpg
7x46mm in 5.56 NATO mag / 7x46 in 7.62 NATO mag
http://i480.photobucket.com/albums/rr169/sgalbra76/7x46120gr2801fpsmuzzle16in100m.jpg
100 meter impact with a 7x46mm 120gr bullet at 2801fps muzzle 16" barrel
With the new modular "multi cartridge" rifles showing up I think this cartridge should have a good chance to get the attention it deserves. New rifles, designed with multiple calibers in mind, like the SCAR, ACR, XCR, the new CZ carabine, could be easily converted to this cartridge.
Once Mr. Murray releases the chamber and case specs, I think we should start buging Magpul to start working on the 30 round mags for it.:D
Back to the future...
I have a case of the 7x49 or 7mm liviano in my hands, and actually Venezuela had their first batch of FALs in this caliber, previous to the 7.62x51 NATO adoption. Based on case capacity, and working at equal pressures, just a tad less powerfull than the 7-08 (2 mm longer case), and a bit more then the 7x46 (which has a 3 mm shorter case and a bit smaller case head). What is better for a MG round, a bit more range and power or a bit less recoil?
I don't think the 7x46 is going to be controlable in full auto, from a light rifle. So it cannot replace the "real" assault rifle rounds like 5.56, 7.62x39, 6.8 SPC, etc. And the round weight is much closer to the 7.62x51 than to the 5.56.
Perhaps some of the Iraq and Afghanistan vets can chime in here......but in the current theater full auto from unstabilized carbines is rarely more effective than semiauto unless it is to clear a room at ranges of only 7-15yrds. At those ranges a 7.62 NATO would get the job done just as well with reasonable muzzle climb. Utilize a proper gas piston with bleed-off, and a well designed muzzle break and the 7.62 NATO is even more controllable. A 7x46mm would fit the part even better. If there is concern about ammo consumption, then a 3-round burst can always be tried. Don't know of any 7.62 NATO rifles that have been tested with a burst.
In terms of fire suppression, larger calibers seem to have better effect in that regard too. 7.62 NATO punches through brick walls pretty well while a 5.56 will only chip at it. Better penetration, better fragmenting distraction, and more of the enemy's cover is disturbed. During WWII the Italians and Japanese both upgraded to 7+mm calibers as they observed weak barrier penetration with their 6.5mm projectiles. Provided that you can keep the ammuntion flow to the troops, a 7mm cartridge will offer many combat benefits that have been absent to infantry in decades.
The problem with the 5.56/6.8/6.5 alternatives is that they don't have very good terminal effects beyond 300m. The 5.56 and 6.8 turn into tumblers, and the 6.5 Grendel likely won't tumble at all before it exits the body. Like the 6.5 Carcano, the very high sectional density of the Grendel and balanced weight distribution causes greatly delayed yaw:
http://i480.photobucket.com/albums/rr169/sgalbra76/CartDev1860_1940.jpg
http://i480.photobucket.com/albums/rr169/sgalbra76/65g_120NFMJ_T145_50_Neck.jpg
Grendel at 100yrds. Notice the greatly delayed bullet upset.
The 7x46 is probably the closest thing to a universal military cartridge right now. At least in its estimated performance.
I don't think recoil is that close to 7x49 Liviano. 7x46 case is based on 7.62x45mm Czech.
The case is wider on 7x49. Close to the .308. 7x46mm used 130gr. bullets instead of 140gr. in Liviano cartridge.
On top of that 7x46 will be loaded at lower pressures from what I understand.
I shot some time ago an old Czech rifle chambered in 7.62x45mm and the recoil was mild.
The 7x49 has a 308 case head, they all descend from the old 7.92x57 round.
Yes, I think the 7x49 should be closer in recoil to the 308 than to the 7x46, but perhaps at this point it is a matter of splitting hairs...
The G3 has one version with 3 round burst, I have tried it (some with this option were bought here in Paraguay) and it works very well. Certainly a FAL/G3 can be shot with decent accuracy (keeping in the torso zone) in short bursts up to 15 yds. But you can also shoot pretty very fast in semi auto, with more accuracy. Perhaps the full auto in these rifles is only useful at closer ranges, < 10 yds , military ambush/stop a car or something like that. Just my thoughts, I'm an engineer and shooting sports fan, but just essentially a civilian that plays with guns, so please don't take it as I'm pontificating on something that is beyond my experience/expertise.
Marcus, it should not be a problem to get a long, sleek, 6.5 mm bullet to yaw fast and fragment, but you should design the bullet to do that (CG offset, weak jacket, etc.), not just pick any match bullet. What bullet is that 6.5 grendel in the gel test? The 123 gr lapua scenar has a lot of empty space up front under the jacket, it should tumble fast, but the jacket is pretty strong.
Marcus, it should not be a problem to get a long, sleek, 6.5 mm bullet to yaw fast and fragment, but you should design the bullet to do that (CG offset, weak jacket, etc.), not just pick any match bullet. What bullet is that 6.5 grendel in the gel test? The 123 gr lapua scenar has a lot of empty space up front under the jacket, it should tumble fast, but the jacket is pretty strong.
That gel shot above was with a 120gr FMJ. It's peak upset was at around 9-10" which in most human torsos has already exited and is unacceptable. The optimal peak upset is around 4"(10cm) of penetration. Bullets with a much heavier rear tend to tumble more quickly.
http://i480.photobucket.com/albums/rr169/sgalbra76/RussianWP.jpg
5.45 does this with a hollow nose. 7.62 M67 does this with a more triangular bullet shape.
Here's the Grendel with a 120gr SMK OTM:
http://i480.photobucket.com/albums/rr169/sgalbra76/65g_120SMK_T16_100yds_Neck.jpg
Peak upset is still around 6-7", and this load tends to perform better than the 123gr Lapua. Other than using an expansion bullet, I haven't seen a Grendel tests that shows it to have acceptable upset in comparison to the 6.8 SPC.
6.8 SPC 115gr SMK OTM:
http://i480.photobucket.com/albums/rr169/sgalbra76/6_8mmRem115grOTM_12in_100m_top.jpg
Peak upset at 3-4". That's about half the distance to peak upset, and probably about 50% overall greater wounding volume than the Grendel through the average human torso which is about 8-9" from front to back.
Unfortunately, I don't have a copy of one of Doc's proposal to the NDIA, but in the 100m windshield shot the 120gr SMK Grendel only penetrated up to 6-7" in gel while the 115gr SMK 6.8 SPC went 14" with good fragmentation. My speculation as to why this occured is because the Grendel must utilize a larger hollow cavity in the nose in order to cause rapid disruption and this weakens the overall design given the limitations on its overall length.
I'm not an engineer, but it seems to me that Bill Alexander was so focused on creating an aerodynamic bullet design with flat tragectory for long range target shooting that he completely ignored the terminal effects of the bullet. That is, when the bullet makes contact with a person it should disrupt as quickly as possible, cause maximum trauma around the 4" mark, and then penetrate to adequate depths through commonly encountered barriers.
The military will probably never go back to exposed lead ammunition as it causes rapid fouling of equipment, particularly in full auto. So, OTM is about the best bullet design at the moment for service use. From my understanding of Murray's work on the 7x46mm.....it is a 6.8 SPC on steroids which upsets quickly, causes a larger wound than 6.8, has a much greater effective range than 6.8, and it will defeat many more barriers than 6.8.
To sum it up:
-The Grendel was first designed as a long range target load, and adapted to improve terminal effects.
-The 6.8 was first designed to maximize terminal effects, and then adapted to perform in likely battlefield conditions.
Thanks Marcus! :)
"I'm not an engineer, but it seems to me that Bill Alexander was so focused on creating an aerodynamic bullet design with flat tragectory for long range target shooting that he completely ignored the terminal effects of the bullet."
Seems probable, in the search for the "round that can replace them all" for light weapons, assault rifle, mid range, sniper round, etc.
But I was just thinking that with a little tweaking (and perhaps sacrificing some of that high BC) 6.5 bullets could be designed for good terminal effect.
Thanks Marcus! :)
"I'm not an engineer, but it seems to me that Bill Alexander was so focused on creating an aerodynamic bullet design with flat tragectory for long range target shooting that he completely ignored the terminal effects of the bullet."
Seems probable, in the search for the "round that can replace them all" for light weapons, assault rifle, mid range, sniper round, etc.
But I was just thinking that with a little tweaking (and perhaps sacrificing some of that high BC) 6.5 bullets could be designed for good terminal effect.
Like I said.....I'm not an engineer, but in order to begin upset the bullet must stop spinning and it must have a force to cause the bullet to flip and have its rear lead. The easiest and more reliable way to do that is to make a more triangular bullet which not only has a heavier rear, but has a very unstable impact. Once it begins its yaw, its deceleration can be so great that it causes the bullet to shear apart once it makes its 90 degree turn......then you have fragmentation. The 6.8 has the ideal FMJ profile that it will actually yaw at around 4-5" and fragment out to about 300m. The OTM version improves it a little by decreasing the peak upset depth and increasing the effective range.
I don't think that the Grendel can be tweaked enough to catch the 6.8 overall, because of its elongated bullet profile that makes it harder to cause unequal weight distribution. The more hollowed out you make the nose in order to cause a rapid yaw, the more fragile the bullet becomes and it becomes a poor barrier penetrator. The Grendel does well with expansion loads......but then again just about any caliber will do well with them too. The ideal defensive rifle caliber in my opinion is one that you can rely on to be effective regardless of what ammunition you get ahold of at the time.
Hehe....I'm sure Doc will come along and correct a lot of what I'm telling you :)
The ideal defensive rifle caliber in my opinion is one that you can rely on to be effective regardless of what ammunition you get ahold of at the time.
I think this is why Mr. Murray went for the 7mm bullet. With larger caliber you don't need so many stars to line up in order to get consistent terminal effects. It also makes a huge difference beyond fragmentation range. You still have a rather large bullet that can get the job done.
I'm not an engineer, but it seems to me that Bill Alexander was so focused on creating an aerodynamic bullet design with flat tragectory for long range target shooting that he completely ignored the terminal effects of the bullet.
Given the fact that the Grendel was not designed as a military round to replace the 5.56 NATO, and given the number of excellent 6.5mm bullets out there, I'm very curious as to what lead you to this conclusion.
-B
More discussion going on here
http://www.68forums.com/forums/showthread.php?t=11001
One of 68forums.com's more active members appears to be overseas with Mr. Murray, he may provide some more insight at a later date.
Given the fact that the Grendel was not designed as a military round to replace the 5.56 NATO, and given the number of excellent 6.5mm bullets out there, I'm very curious as to what lead you to this conclusion.
-B
Nothing wrong with the 6.5 caliber size. In order to meet the Grendel's OAL requirements, and still keep enough crimp for solid seating, the Grendel needs to maintain the elongated bullet design which is great for long range shooting......bad for rapid yaw. You can tweak the bullet with a hollow nose, but that sacrifices barrier penetration ability. Alexander did not do any professional terminal effects testing in the development of his load......thus he was focused primarily on punching holes in paper.
The 6.5 has been a good medium game taking in Europe with either exposed lead bullets or soft points. Every rifle caliber does well with expansion loads and the Grendel is no exception. I would not be surprised that in Alexander's selection of the elongated 6.5 bullet, he assumed it was effective based on the long history of it being an effective hunting cartridge in Europe........this of course based on the exposed lead nose or solid lead bullet. In terms of actual service use with a wide variety of Hague compliant bullets such as FMJ and OTM, the Grendel does not do as well as either the 6.8 or 7x46.
Here's that presentation of Doc's in 2008. Page 15 has the Grendel OTM versus windshield test and demonstrates how it breaks up easily against the barrier.
http://www.dtic.mil/ndia/2008Intl/Roberts.pdf
In order to get rapid upset and fragmentation out of the OTM Grendel, the bullet needs significantly more hollow space in the nose which makes it fragile. The Grendel definately has its place in the market, but in my opinion not in a general issue military cartridge.
Interesting. The physics of what you're saying is a little fuzzy to me; the Grendel has a greater sectional density than the .308, so penetration should be more reliable. Additionally, those long Scenar and VLD bullets are back-heavy, meaning they want to tumble after entering a medium; virtually all such rounds have been used very successfully while hunting, even though they're basically long, skinny, and weird shaped FMJs. Grendelizor's post here (http://www.ar15.com/lite/topic.html?b=3&f=121&t=271627) (third post, I think, starting with ammo box pictures) showed tests conducted by Speer, in accordance with FBI and in-house standards, that demonstrated pretty good expansion with pretty good penetration in gel. If this article (http://www.65grendel.com/art004balltests1.htm) has any merit (no source leaves me skeptical), a heavier FMJBT Grendel load did pretty darn well in FBI testing. With all due respect to Dr. Roberts, the linked pdf only demonstrates an image of one Grendel load (not the preferred one by many advocates of the round), and otherwise ignores the cartridge altogether.
For what it's worth, I have no dog in this fight. I'm not particularly interested in either the 6.5 Grendel or 6.8 SPC. As a civilian, I'm well served by the 5.56x45. As a taxpayer, I'd rather we built the next issue service rifle around the cartridge than the other way around, so I don't much care for the idea of limiting our options to the AR-15 mag well. But if we're going to compare in an apples to apples manner then I like seeing even, fair comparisons. 1) Take ten each of the top five loads for both the Grendel and SPC. 2) Line 'em up and measure external ballistics at muzzle, 50y, 100y, 200y, 500y, and 800y. 3) Then line 'em up and measure terminal ballistics in accordance with FBI testing. 4) Let the data speak for itself.
-B
Burt Gummer
12-22-09, 12:03
Why not just further develop the 7mm-08? The caliber is already well established. 7.62x51 rifles can be readily be adapted by a barrel swap. Maybe Hornady can develop a 120gr. AMAX bullet for this purpose?
Interesting. The physics of what you're saying is a little fuzzy to me; the Grendel has a greater sectional density than the .308, so penetration should be more reliable. Additionally, those long Scenar and VLD bullets are back-heavy, meaning they want to tumble after entering a medium; virtually all such rounds have been used very successfully while hunting, even though they're basically long, skinny, and weird shaped FMJs. Grendelizor's post here (http://www.ar15.com/lite/topic.html?b=3&f=121&t=271627) (third post, I think, starting with ammo box pictures) showed tests conducted by Speer, in accordance with FBI and in-house standards, that demonstrated pretty good expansion with pretty good penetration in gel. If this article (http://www.65grendel.com/art004balltests1.htm) has any merit (no source leaves me skeptical), a heavier FMJBT Grendel load did pretty darn well in FBI testing. With all due respect to Dr. Roberts, the linked pdf only demonstrates an image of one Grendel load (not the preferred one by many advocates of the round), and otherwise ignores the cartridge altogether.
For what it's worth, I have no dog in this fight. I'm not particularly interested in either the 6.5 Grendel or 6.8 SPC. As a civilian, I'm well served by the 5.56x45. As a taxpayer, I'd rather we built the next issue service rifle around the cartridge than the other way around, so I don't much care for the idea of limiting our options to the AR-15 mag well. But if we're going to compare in an apples to apples manner then I like seeing even, fair comparisons. 1) Take ten each of the top five loads for both the Grendel and SPC. 2) Line 'em up and measure external ballistics at muzzle, 50y, 100y, 200y, 500y, and 800y. 3) Then line 'em up and measure terminal ballistics in accordance with FBI testing. 4) Let the data speak for itself.
-B
The testing that Grendelizer has been promoting was NOT done by CCI Speer. It was performed by an ammunition distributer that happens to sell Speer ammunition. Also, he may have claimed to have used FBI protocols, but the very pictures themselves demonstrate that he did not do so. FBI protocols do not use colored dye which can alter the consistancy of the ballistic gel, and in the pictures a calibration BB would be clearly observed in the dye which he did not use either. So, these blocks of gel used dye which may have altered the density and elasticity of the gel, and it was never calibrated to determine if it was up to standards. You can read more on proper FBI testing techniques in Duncan MacPherson's book "Bullet Penetration". So, be skeptical of the results.
Doc believes that the Grendel is a better alternative to the 5.56. However, I have never seen a FMJ or OTM Grendel load that can disrupt more quickly than the 6.8 SPC.
Barrier penetration is not only a function of sectional density, but of bullet construction. Other than good velocity, a FMJ or OTM bullet needs two things to fragment. It needs a very unequal weight distribution(heavier rear), and a weak enough bullet jacket to shear apart after the bullet yaws 90 degrees. A triangular bullet design like the M67 or 6.8 SPC requires little empty space in the nose in order to have enough rear weight distribution to yaw quickly. The Grendel needs almost 1/4-1/3 of its overall bullet length dedicated to a hollow cavity in order to have rapid upset. Once the bullet impacts a barrier the jacket pulls off the nose more quickly and the bullet comes apart prematurely. OTM have always done poorly in 5.56 against windshields, and the Grendal seems to do similarly. The Russian 5.45x39 which utilizes a hollow nose also does very poorly against windshields and many Russian special forces units have opted to use the older 7.62x39 in a M67 loading that tumbles based on a tear drop bullet shape.
The 6.8 SPC is one of the few calibers that can:
-Penetrate to ideal depths through a windshield at 100m while fragmenting
-Reach peak disruption at only 3-4" of penetration depth
.......and all this from an OTM load. Why?....because it maintains an ideal tear drop bullet profile which disrupts quickly regardless of how what load you use.....and it doesn't require the weaknesses of a hollow nose. FMJ does well, OTM does well, ballistic tips do well, and good ole soft points do well. Why field the Grendel which from all professional testing only does as well as the other alternatives with a ballistic tip or expansion load?
The 7mm-08 is still as long as its parent cartridge, right? There's a good description I read here (http://www.65grendel.com/forum/showpost.php?p=10548&postcount=36) that might explain the reluctance to move to a heavier gun. (Short and sweet of it is that everyone loves the way the AR handles, so something that's a little better than the 5.56, but that is also light, has minimal recoil, and can be handled by a light gun would be ideal.)
I've heard only good things about the 7mm-08, but if it requires an AR-10 to run it I'd have a hard time asking our warfighters to put up with just a few more pounds...
-B
Just to add. Be care in comparing hunting success with use against people. The most common shot on any four legged animial is a flank shot which if placed correctly in the thoracic cavity will punch through both lungs and the heart and/or aorta. Against a human adversary most shots are through the front of the torso which sections off your kill zone into quadrants. It is much easier to rapid drop an animal through a flank hit to the thoracic cavity than a frontal hit and it can be confusing as to which caliber and load is a better performer. On an abdominal hit on a deer, you only have a small section of a flank hit in which to hit the spine or aorta. On a human frontal hit you have a greater probability of hitting those regions.
Heavy Metal
12-22-09, 12:32
Perhaps some of the Iraq and Afghanistan vets can chime in here......but in the current theater full auto from unstabilized carbines is rarely more effective than semiauto unless it is to clear a room at ranges of only 7-15yrds. At those ranges a 7.62 NATO would get the job done just as well with reasonable muzzle climb. Utilize a proper gas piston with bleed-off, and a well designed muzzle break and the 7.62 NATO is even more controllable. A 7x46mm would fit the part even better. If there is concern about ammo consumption, then a 3-round burst can always be tried. Don't know of any 7.62 NATO rifles that have been tested with a burst.
In terms of fire suppression, larger calibers seem to have better effect in that regard too. 7.62 NATO punches through brick walls pretty well while a 5.56 will only chip at it. Better penetration, better fragmenting distraction, and more of the enemy's cover is disturbed. During WWII the Italians and Japanese both upgraded to 7+mm calibers as they observed weak barrier penetration with their 6.5mm projectiles. Provided that you can keep the ammuntion flow to the troops, a 7mm cartridge will offer many combat benefits that have been absent to infantry in decades.
The problem with the 5.56/6.8/6.5 alternatives is that they don't have very good terminal effects beyond 300m. The 5.56 and 6.8 turn into tumblers, and the 6.5 Grendel likely won't tumble at all before it exits the body. Like the 6.5 Carcano, the very high sectional density of the Grendel and balanced weight distribution causes greatly delayed yaw:
http://i480.photobucket.com/albums/rr169/sgalbra76/CartDev1860_1940.jpg
http://i480.photobucket.com/albums/rr169/sgalbra76/65g_120NFMJ_T145_50_Neck.jpg
Grendel at 100yrds. Notice the greatly delayed bullet upset.
The 7x46 is probably the closest thing to a universal military cartridge right now. At least in its estimated performance.
To be fair, the Carcano load is a round nose.
To be fair, the Carcano load is a round nose.
Yep. Just an example of using an elongated bullet profile which has a harder time trying to flip over verses a shorter bullet. The Grendel FMJ load still would have exited the body in a frontal shot before it yawed enough to tumble.
The testing that Grendelizer has been promoting was NOT done by CCI Speer. It was performed by an ammunition distributer that happens to sell Speer ammunition. Also, he may have claimed to have used FBI protocols, but the very pictures themselves demonstrate that he did not do so. FBI protocols do not use colored dye which can alter the consistancy of the ballistic gel, and in the pictures a calibration BB would be clearly observed in the dye which he did not use either. So, these blocks of gel used dye which may have altered the density and elasticity of the gel, and it was never calibrated to determine if it was up to standards. You can read more on proper FBI testing techniques in Duncan MacPherson's book "Bullet Penetration". So, be skeptical of the results.
Best thing about being a college student is I'm always skeptical of results. :D Still, I'd like to hear John's side to that.
Doc believes that the Grendel is a better alternative to the 5.56. However, I have never seen a FMJ or OTM Grendel load that can disrupt more quickly than the 6.8 SPC.
We also haven't seen any honest multi-faceted head-to-head comparisons either. Which annoys me, since it's not hard to do...
If I remember correctly, Dr. Fackler has described fragmentation as an unreliable wounding mechanism. We know how it happens, but inducing consistent (amount) and reliable (frequency) fragmentation is historically hard to do. Again, I point to the large number of shooters who regularly take game of all sizes with Scenar and VLD-type 6.5mm bullets. It's pretty plain that they perform well in both target and hunting capacities. As for auto glass... Given how poorly the SMK and TSX bullets fare against auto glass, I'm curious how well these longer/skinnier bullets will do. I don't think anybody's ever tested them.
Why field the Grendel which from all professional testing only does as well as the other alternatives with a ballistic tip or expansion load?
That's silly. What all has "professional testing" tested? From what I'm reading it's very little: a 120gr SMK and a 144gr FMJBT. If you have data on any number of the other 6.5mm bullets available that would be JAG-approved, by all means... ;)
-B
Burt Gummer
12-22-09, 15:44
The 7mm-08 is still as long as its parent cartridge, right? There's a good description I read here (http://www.65grendel.com/forum/showpost.php?p=10548&postcount=36) that might explain the reluctance to move to a heavier gun. (Short and sweet of it is that everyone loves the way the AR handles, so something that's a little better than the 5.56, but that is also light, has minimal recoil, and can be handled by a light gun would be ideal.)
I've heard only good things about the 7mm-08, but if it requires an AR-10 to run it I'd have a hard time asking our warfighters to put up with just a few more pounds...
-B
Wouldn't 7x46mm require a larger platform anyway?
Wouldn't 7x46mm require a larger platform anyway?
Yes. The 7x46mm has an OAL about half way between the 5.56 and the .308:
Base Diameter 6.8 = 0.421" ; 7mm Murray = 0.441" ; 308Win = 0.470"
Case Length 6.8 = 1.676" ; 7mm Murray = approx 1.85" ; 308Win = 2.015"
Overall Length 6.8 = 2.30" ; 7mm Murray = 2.50" ; 308Win = 2.80"
So, smaller case diameter than the .308, and a shorter OAL. Dimension-wise, it's actually closer to the 5.56/6.8/Grendel in required platform size than the .308.
Like Marcus said, something between the AR-15 and AR-10, size-wise, so yeah. I'm more inclined to agree with that dude on 65Grendel who I linked to earlier: something with a bit more punch than the 5.56, that can do it at longer ranges, and keeps the light recoil, ammo, and weapon weight of what's currently had. The 7x46 may be a great round in its own right, but I'm not sure if it's a needed one (I know, I know, let me explain). If we're discussing a new replacement military round, we're supposed to be learning the lessons of previous cartridges and weapons throughout history, right?
Well, we know the .308 to be too much for a standard-issue cartridge right now: heavy, greater recoil (reduced speed of follow-up shots), necessitates heavier guns, reduced capacity for the same weight, etc. BUT! The .308 also does good things downrange when things need doing and handles barriers well. We know the 5.56x45 is not quite enough: it does a good job killing, and can kill at distance, but it's very sensitive to AOA and velocity differences, is not very good with barriers. BUT! It's light, has very low recoil (greater speed for follow-up shots), allows for lighter guns, greater ammo capacity for the same weight, and is pretty accurate. All of these tie heavily with the weapon systems employed. People like the AR-15. It's light, carries well, maneuvers well, and is durable and reliable (with proper maintenance). They want a little more out of the cartridge; not a whole lot, but something with longer legs, that handles barriers better, and is less sensitive to variables.
Would the 7x46 cartridge allow for a rifle that's still fairly light while also being durable and reliable, still have fairly mild recoil, not significantly reduce the warfighter's ammo capacity, and perform better than the 5.56 at longer ranges and vs barriers? I think the last one's a given (7mm pretty well rocks...), but the first few I'm not sure about. At face value it seems like a round more destined to replace the .308 in military use than the 5.56, and I really don't see a single 'universal' round being adopted given current bullet/powder/cartridge technology.
-B
Well, we know the .308 to be too much for a standard-issue cartridge right now: heavy, greater recoil (reduced speed of follow-up shots), necessitates heavier guns, reduced capacity for the same weight, etc. BUT! The .308 also does good things downrange when things need doing and handles barriers well. We know the 5.56x45 is not quite enough: it does a good job killing, and can kill at distance, but it's very sensitive to AOA and velocity differences, is not very good with barriers. BUT! It's light, has very low recoil (greater speed for follow-up shots), allows for lighter guns, greater ammo capacity for the same weight, and is pretty accurate. All of these tie heavily with the weapon systems employed. People like the AR-15. It's light, carries well, maneuvers well, and is durable and reliable (with proper maintenance). They want a little more out of the cartridge; not a whole lot, but something with longer legs, that handles barriers better, and is less sensitive to variables.
This is all true. Weight is the predominant factor in moving up in caliber, and the military is obsessed with keeping the overall weight of the soldier down......just as they should. To go with the 7x46 you'd have to sacrifice about 1/3 less in ammunition to keep the weight down, and better control your depletion of ammo. 20-25rd magazines will also help as it is a tendency during combat stress to keep firing on an enemy even though they have dropped and are no longer a threat. The same happens in law enforcement when the officer empties his magazine on a perp when the first 5 shots got the job done and the rest are insurance as a result of combat stress the the automatic repeated pulling of the trigger. Needless to say, full auto tends to waste more ammo than anything else with limited benefits from the regular infantry soldier. Given that we maintain good logistics and supply lines, I don't see a problem in fielding the 7x46 for general issue. Over extending your stay is usually a problem with incompetent commanders.
However, sometimes the right tool just weighs a little more and as you mentioned in historical lessons the militaries of the world in the 20th century have tended to go with light calibers during peace time and when a conflict occurs they jump back to something heavier. Good examples were the Italians in WWII who went from the 6.5 to the 7.35, and the Italians who went from the 6.5 to the 7.7. The Russians have also been toying with modernizing the 7.62x39, as well as using the 9x39 more. Once you get down good terminal effects and range, then you need to take into account the defeat of commonly encountered barriers. The FBI protocols are good start, but in a military conflict you have stronger barriers such as walls, sand bags, rock, and other materials. One test I saw with the Russian 9x39mm, it pentrated through a telephone pole and then through the front and back of a level III vest. The heavier and faster your projectile, the more likely your shot will penetrate the barrier or knock enough of it away to expose the enemy. The Italians and Japs though that their 6.5mm rifles didn't do a good enough job in this regard.
The problem with the Italy/Japan analogy is that it's not especially analogous. The 6.5x52 pretty well sucked because of bullet design and inconsistent powder quality. Italy also didn't have the industry to support a total war. The easy solution was to switch calibers to match with their allies. The Japanese wanted to replace their very old 6.5x50 after watching the success of the .303 British (the 7.7x57's parent case) and the 7.92x57 Mausers used by the Chinese a few years before the start of WWII. I don't think it would be accurate to say that these nations switched calibers because the 6.5mm prove ineffective.
Anything that we do is going to be heavier; the 5.56 is a light MFer. The hard part is going to be keeping the weight down to what's necessary. Question: can we accomplish what we need to in our current conflicts, and what we suspect to be our future conflicts, with one "universal" caliber? I don't really know, but I doubt it. We're talking about replacing both the 249 and 240 with a single machine gun (pretty big deal). We're talking about making our sniper ammo the same as our fighting rifle ammo (maybe a big deal; not sure how often snipers have had to delink machine gun ammo to use in combat). These are huge proposed changes. Even the Chinese, who may have the most modern current-issue assault rifle ammunition, still retained distinct "light" and "medium/general purpose" machine guns. I don't see what adopting a "universal" round would add in capability as opposed to replacing just the 5.56 with a slightly better round, probably in the 6mm range.
-B
I don't think the 7x46UAC needs to replace the 7.62 entirely. We could keep the .308 in fixed positions and vechicles, aircraft and use the 7x46 for everything that has to be humped by the troops. Sniper rifles can keep their specialized cartridges. For DMR I think the 7x46mm could be just fine.
When talking about the weight of the ammo you have to look at everyone out there that fields 7.62x39 weapons. They do just fine with the ammo they can carry. 7x46 is based on the same case. It is closer to the Russian round than .308 in weight, so i doubt it would be too much for the troops.
If thirld world skinny and hungry troops can carry the ammo for their AK's so can ours.
The true is that our troops carry a lot of other stuff that weights them down. The weapon and ammo is a very small percentage of the weight our troops carry.
On the other hand you have to look at the weight problem as a whole. Starting with Iraq war#1 a lot of heavier weapons have been introduced to compensate for the limitations of the 5.56. That is also weight that has to be deployed. With the 7x46mm as main cartridge you don't need most of those. What that round can't reach or can't penetrate will most likely be just as hard to kill with the 308.
What's interesting is that even Dr. Roberts seems to agree that the 7x46 is more related to the 7.62 than the 5.56 (as a larger cartridge), indicated by his parting comment here (https://www.m4carbine.net/showthread.php?t=19936). I think it's pretty clear that a 7x46 would require a larger weapon system more akin to the AR-10 than the AR-15. It would also be prudent to note that no modern military has returned to these larger "battle rifle" dubbed calibers. I believe this in itself speaks volumes.
Jaws, do you know how much ammo militaries employing the 7.62x39 carry on average? How much other gear are they also carrying, and what do we think the total weight is? Do they traditionally fight close to supply lines or do they expand from them? Additionally, perhaps most importantly, what success have these militaries seen compared to nations that have moved toward the lighter 5.56 NATO? I find it hard to believe we can draw any kind of meaningful conclusions from looking at at the ammo alone, or even the ammo + weapon.
I find it interesting that the SDM program seems to feel the 5.56 is fine for the role. This seems to indicate that there is an expectation that troops will need something at the squad level that can reach out accurately but maintain the 5.56 NATO loadout rather than bump up to the 7.62. This appears to indicate that our fightin' folks are happy with their .30-cal weapon systems in their current capacity, which would mean that if something ought to be improved it should probably just be the 5.56. Maybe there are some finer elements that I'm missing as a civilian...?
(NOT trying to be argumentative; just trying to promote meaningful dialogue on a subject of interest to those whom it would directly effect and to others, like me, who find the topic fascinating in its own right.)
-B
Jaws, do you know how much ammo militaries employing the 7.62x39 carry on average? How much other gear are they also carrying, and what do we think the total weight is? Do they traditionally fight close to supply lines or do they expand from them? Additionally, perhaps most importantly, what success have these militaries seen compared to nations that have moved toward the lighter 5.56 NATO? I find it hard to believe we can draw any kind of meaningful conclusions from looking at at the ammo alone, or even the ammo + weapon.
Not Jaws....but out of nearly 100 different countries that have fielded the AK-47, you can find over 100 different carry compliments. The Soviets fielded AK-47s to front and second line troops as well as special forces. In general, second line troops carried the least, front line carried more, and special forces usually carried the most. A lot of special forces carried the 6-mag pouch on their chest(210rds), and sometimes this carried over to the front line troops. A lot of second line troops carried only two additional magazines for a total of 90rds. Not sure on the ammo compliment for light machine guns like the RPK, but it probably averaged around 300-500rds.
At least in the current wars in Iraq and Afghanistan, the need for carrying high volumes of ammo for the standard infantry soldier hasn't been a big deal. Some of our guys have packed in 400rds or so and rarely gone beyond 100rds. Special operations is another matter in which they dump high volumes of fire during in an assault and most will carry 800+rds.
Either way, it is rare for infantry engagements to occur beyond 400m.....even in the mountains of Afghanistan. This chart is from the 2003 DOD briefing on infantry combat ranges:
http://i480.photobucket.com/albums/rr169/sgalbra76/riflechart.jpg
The problem in Afghanistan was that the 5.56 was not exhibiting reliable terminal effects at any range, and it had poor barrier penetration. The USAMU and USSOCOM combined effort to create a better cartridge yielded the 6.8 SPC and the 7x46. The 6.8 SPC was ideal if working within the M4 platform, and the 7x46 was optimal if going on no platform restrictions.
From the 7x46 DrGKR post:
https://www.m4carbine.net/showthread.php?t=19936
The 7x46 launches a 120 gr bullet at 2805 fps from a 16" barrel, A LOT closer to 7.62x51 (NATO ball = 147 gr @ 2600 fps from this barrel length) than to 5.56x45 (M855 = 62 gr @ 2950 fps). Nice load!!
The 7x46 case has a volume a little closer to the 6.8 SPC than to the 308, but again MUCH closer to the 308 than to the 5.56.
A quick recoil impulse comparison (powder charges just estimations):
7.62x51: 147 gr @ 2600 fps, 44 gr powder = 2.44 lb-sec (100% - baseline)
7x46: 120 gr @ 2805 fps, 36 gr powder = 2.13 lb-sec (87%)
6.8 SPC: 115 gr @ 2580 fps, 29 gr powder = 1.83 lb-sec (75%)
5.56x45: 62 gr @ 2950 fps, 25 gr powder = 1.26 lb-sec (52%)
Here's a logistics calculation on ammunition weight:
-5.56 NATO 62gr: 300rds = 7.9lbs
-6.8 SPC 115gr: 300rds = 11.3lbs
-7.62x39 M67 123gr: 300rds = 11.6lbs
-7.62 NATO 147gr: 300rds = 16.5lbs
Supplying a front line force?
-5.56 NATO 62gr: 1,000,000rds = 13.23tons
-6.8 SPC 115gr: 1,000,000rds = 18.9tons
-7.62x39 M67 123gr: 1,000,000rds = 19.4tons
-7.62 NATO 147gr: 1,000,000rds = 26.6tons
Just to throw some more resources out there, here's the DTIC presentation from Schatz:
http://www.dtic.mil/ndia/2008Intl/Schatz.pdf
Mostly it addresses the US military's problem with adopting new equipment for incremental advantages. It also has some information regarding the advantages of adopting a larger caliber than 5.56.
Here's a logistics calculation on ammunition weight:
Nice comparison, Marcus!
-5.56 NATO 62gr: 300rds = 7.9lbs
-6.8 SPC 115gr: 300rds = 11.3lbs
-7.62x39 M67 123gr: 300rds = 11.6lbs
-7.62 NATO 147gr: 300rds = 16.5lbs
300 rds 7x46 should be around 13.8 lbs?
Supplying a front line force?
-5.56 NATO 62gr: 1,000,000rds = 13.23tons
-6.8 SPC 115gr: 1,000,000rds = 18.9tons
-7.62x39 M67 123gr: 1,000,000rds = 19.4tons
-7.62 NATO 147gr: 1,000,000rds = 26.6tons
1,000,00 rds 7x46 should be around 22.6 tons?
1,000,00 rds 7x46 should be around 22.6 tons?
I have no idea of the overall weight of the 7x46. There isn't a concensus on bullet weight or charge weight either as of yet. It would probably be in that ballpark though.
Then it really does sound more like a cartridge to compete with the 7.62N than the 5.56N. Similar ballistics and recoil impulse, guestimated weight and size closer to the 7.62N end than the 5.56N end, etc. I agree that adopting a larger caliber than the 5.56x45 is a good idea, but adopting something only a little smaller than the .308? I really like what the 6mm AR and 6mm AR Turbo bring to the table, but we're only talking 3k-4k barrel life out of SS barrels, maybe twice that out of chrome-lined barrels (definitely unsat).
That 2003 chart also seems to indicate that recoil impulse is pretty important for getting rounds on target (supporting the fellow I quoted/linked-to earlier). It should also be pointed out that this is before the adjustments in how our Coalition troops are being fought in Afghanistan (longer and longer ranges, staying just inside mortar and RPG range but out of rifle range, etc.); I wonder if the curve would be the same now as it was in 2003.
Does the 7x46mm have a unique case head size? If so I've an idea (http://www.snipercentral.com/forums/viewtopic.php?t=28826) I've been tossing around that I'd like to compare it to, just for shits and giggles.
-B
From: https://www.m4carbine.net/showthread.php?t=19936
"Since the 7 x 46 mm is based on the proven Czech military 7.62 x 45 mm cartridge (itself an offshoot of the Russian 7.62 x 39 mm), it has an established record feeding and functioning in both magazine and belt-fed full-auto fire. Likewise, recoil appears manageable and weapons remain controllable in FA fire, just as with the Czech cartridge. Like the 6.8 mm, the 7 x 46 mm is optimized for shorter barrels and larger magazines than the heavier, bulkier, and harsher recoiling 7.62 x 51 mm/.308 cartridge."
7 x 46 mm feels a lot more like shooting a 7.62x39 mm than a 7.62x51 mm. The case head is the same as the 7.62x39 mm or 6.5G. The cartridge OAL seems exactly in between 5.56 mm and 7.62x51mm. Thus magazines would be similar in most dimensions to those for 7.62x39 mm or 6.5G, except being a bit longer stem-to-stern, as noted below in a picture comparing 7 x 46 mm cartridges inserted into both an AR15 mag and an M14 mag:
http://i459.photobucket.com/albums/qq319/DocGKR/7x46inmags.jpg
Keep in mind a lot of bullet diameters were tested as part of the SPC development, including 6 mm and 6.5 mm ones:
http://i459.photobucket.com/albums/qq319/DocGKR/SPC_trials.jpg
In general, 6 mm ones did poorly against intermediate barriers compared to larger projectiles; 6.5 mm ones did not upset as rapidly or prove as destructive as the 6.8 mm and 7 mm ones.
In Afghanistan more then 50% of engagements are between 300m and 800m.
http://www.quarry.nildram.co.uk/btb.pdf
That 2003 chart also seems to indicate that recoil impulse is pretty important for getting rounds on target (supporting the fellow I quoted/linked-to earlier). It should also be pointed out that this is before the adjustments in how our Coalition troops are being fought in Afghanistan (longer and longer ranges, staying just inside mortar and RPG range but out of rifle range, etc.); I wonder if the curve would be the same now as it was in 2003.
The curve is only partically based on technology, it is mostly based on the abilities of the human body. Hand eye cooridination, vision, steadying the weapon platform, and the ability to mentially calculate trajectory and lead. So, these figures have been in effect for pretty much all of the 20th century. Even during the trench wars of WWI, the average engagement range for standard infantry was still only at 300-400m. The ranges got even shorter in WWII in which the Germans recognized it and produced the 7.92x33. Both the US and Soviets thought that they could extend that range a bit with flatter shooting 5.56 and 5.45, but the engagement ranges remained virtually unchanged for regular infantry.
If you have moving enemy infantry at 600m, then the best way to deal with them is with a medium machine gun which will pepper the area, mortars, or air strikes. This is why improved terminal effects at ranges up to 300m are what's in demand by the military for regular infantry. Anything beyond 300m is best left to special weapons teams who can more effectively get the job done at those ranges.
Back to the 6.8 SPC and 7x46. They were never really intended to be used at over 500m unless they were being used by sniper teams or medium machine guns. In that regard, the 6.8 SPC and Grendel are a little weak in comparison to the 7x46 or .308. The 6.8 was setup to be an improved infantry caliber. The 7x46mm was designed to be a heavier hitting infantry caliber, but powerful enough to also be used by special weapon teams at longer ranges. A true universal cartridge.
In Afghanistan more then 50% of engagements are between 300m and 800m.
http://www.quarry.nildram.co.uk/btb.pdf
The primary reason why those ranges have increased is due to insurgent sniper attacks. So, they are initiated by special weapons teams at ranges beyond typical infantry combat ranges. In guerrila warfare the enemy usually initiates the attack from a position of advantage. In Vietnam that advantage was up close and personal with high volumes of fire by regular infantry. In Afghanistan that position of advantage is at ranges beyond typical infantry combat ranges with their own special weapons teams.
So, what we are comparing here is special weapon team engagement ranges......not infantry engagement ranges.
7 x 46 mm feels a lot more like shooting a 7.62x39 mm than a 7.62x51 mm.
Perhaps this "feel" is due to the plattform, not the actual recoil impulse of the round:
7.62x51: 147 gr @ 2600 fps, 44 gr powder = 2.44 lb-sec (100% - baseline)
7x46: 120 gr @ 2805 fps, 36 gr powder = 2.13 lb-sec (87%)
6.8 SPC: 115 gr @ 2580 fps, 29 gr powder = 1.83 lb-sec (75%)
7.62x39: 123 gr @ 2330 fps, 25 gr powder = 1.72 lb-sec (70%)
5.56x45: 62 gr @ 2950 fps, 25 gr powder = 1.26 lb-sec (52%)
Where did you find the 36gr of powder for the 7x46 round? I know the old 7.62x45 used around 29gr. Pretty much the same case.
7X46 would be great as a main rifle, machinegun, LMG, and DMR.
6X35 would be great for PLs, PSGs, RTOs, and as a backup for anyone who should be working or thinking more than shooting.
8.56 would be great for snipers and vehicle mounted MGs.
8.56 = .338? Would that be replacing the .50 as a heavy machine gun?
-B
Yes. For all it's romance the M2 is on the way out and the replacement will fire only 250 rounds per minute. A better idea would be to load the Lap to 3.9 inches with APIT and use it in bolt action rifles and the 240.
Where did you find the 36gr of powder for the 7x46 round? I know the old 7.62x45 used around 29gr. Pretty much the same case.
It is a guesstimation... the 6.8 SPC (much smaller case than the 7.62x45) uses about 29-30 gr of powder. The old 7.62x45 uses only 29 gr because it is relatively fast burning. In order to achieve the very high velocities claimed by the 7x46, most probably a slower powder must be used.
In any case, I would guess that the powder charge is at least 10% more than the 6.8 SPC, and it doesn't make much difference in the recoil impulse comparison:
7.62x51: 147 gr @ 2600 fps, 44 gr powder = 2.44 lb-sec (100% - baseline)
7x46: 120 gr @ 2805 fps, 36 gr powder = 2.13 lb-sec (87%)
7x46: 120 gr @ 2805 fps, 33 gr powder = 2.08 lb-sec (85%)
Perhaps DcGKR can confirm if we are in the ballpark.
It sounds like we're getting most of the .308 with the 7x46... :confused:
-B
I don't think recoil is that close to the .308.
Is that 2600fps corect for the 147gr 7.62x51mm NATO?:confused: It looks more like velocity for heavier rounds.
I found this info for the M80 ball:
Bullet: 147 grain FMJ
Powder: 46 grains WC846, 41 grains IMR 4475, or 41.5 grains IMR 8138
Velocity = 2750 +/- 30 fps @ 78 ft.
Pressure = 50,000 psi max average.
Burt Gummer
12-24-09, 15:03
I feeling there's no love for the .308 around here.
I for one, prefer the 7.62x51mm cartridge, and would gladly have traded my issue M16A2 (I'm dating myself here) for a .30-caliber rifle back in my day as an 0311.
Over the years, I've been saving quotes from DocGKR in various forums about some of his opinions (Dr. Roberts, please correct me if your views have changed since you made the following statements)...
There are NO 5.56 mm bullets which produce damage anywhere near what the .308 polymer tip bullets, such as the 155 gr AMAX and 150 gr Nosler Ballistic Tip, cause at close range; these projectiles are among those most likely to cause rapid incapacitation when you absolutely, positively need to cause immediate cessation of hostile activity when confronting a threat which mandates the use of lethal force.
—Dr. Gary K. Roberts 01-14-2003
If I knew for certain I was going to be in harm’s way on a given day and had the luxury of preparing for the encounter, neither 5.56 mm, 6.8 mm, nor 7.62x39mm would be first on my list--I would unhesitatingly choose to use a compact 16-18” barrel .308/7.62x51 mm rifle, like an M14 SOPMOD-EBR/M1A, DSA FAL, the new Robinson Arms SCAR-H, or a .308 AR type carbine (assuming it is a reliable one), firing Hornady 155 gr AMAX or Nosler 150 gr Ballistic Tip, as this combination has the greatest likelyhood [sic] of rapidly incapacitating an opponent over a wide variety of circumstances and potential engagement scenarios. Keep in mind that .308 is much better at penetrating intermediate barriers and shooting into vehicles than 5.56 mm, 6.8 mm, or 7.62x39mm.
—Dr. Gary K. Roberts 03-05-2004
The PD here presented a SWAT carbine school this week. After teaching my section of the course, I decided to stick around and run through the rest of the day's drills and tests with the students. However, instead of using an optic equipped 6920 like normal, I chose to run an old school, iron sighted, CA civilian legal, 18" M1A that had all the crappy SA parts replaced with USGI ones (we have seen a lot of recent SA M1A's fail in classes, especially the 16" barrel SOCOM's due to poor parts quality). Last time I shot a SWAT course with iron sights was back in 2000 with a Colt 6520 carbine. The young studs were giving me a hard time about my old "musket"...until we started shooting. I was surprised how well things went--dumping 20 rounds into a stationary head size target at 100 m was easy, close in CQB drills and shooting on the move went well, and some scenario based tests (including simulated one arm injuries) posed no problems. The one area that could potentially be an issue was the safety location--this is a huge liability area for an LE rifle. The rifle fired 500 rounds of 155 gr Hornady AMAX with no failures to feed or function. All-in-all, I prefer an AR15, but it was interesting to see how well the old dog (both the rifle and me) could run and it was a lot of fun! If a viable modern designed 7.62x51 mm carbine ever makes it to the market, for example the FN Mk17 SCAR-H, I might consider switching over from an AR15 for the superior terminal performance offered by the 7.62x51 mm cartridge.
—Dr. Gary K. Roberts 10-07-2008
I wouldn't drive the last nail in the coffin for the 7.62x51mm being viable as a modern battle rifle (and I'm not talking about DM designated roles either):
http://www.thefirearmblog.com/blog/wp-content/uploads/2009/11/091106a_6005m_002-tfb-tm.png
There's even been a sighting of Chris Costa (http://lightfighter.net/eve/forums/a/tpc/f/7206084761/m/197107144) running a SR-25 in a MagPul Dynamics class.
Yes, mission drives gear, but I still see a the 7.62x51mm as a legitimate fighting platform and not just relegated to sniping. [Flame suit on]
I don't think recoil is that close to the .308.
Is that 2600fps corect for the 147gr 7.62x51mm NATO?:confused: It looks more like velocity for heavier rounds.
I found this info for the M80 ball:
Bullet: 147 grain FMJ
Powder: 46 grains WC846, 41 grains IMR 4475, or 41.5 grains IMR 8138
Velocity = 2750 +/- 30 fps @ 78 ft.
Pressure = 50,000 psi max average.
That's the velocity for a 21" barrel, to compare apples to apples I estimated the velocities of all rounds in a 16" barrel :)
I feeling there's no love for the .308 around here.
The bigger and faster the round the better in my opinion. It's a great cartridge when you are shooting it out of a 21" M14, but you sacrifice a lot when you get down to 16" or shorter barrels. The .308 burns off a large about of charge out the muzzle of shorter barrels resulting in a lot of wasted charge and exponentially slower bullet velocties. Shorter barrels are becoming the norm now days. The military are using vehicles more and more, and then of course law enforcement are in and out of vehicles requiring a short enough weapon to easily clear door frames and hatches. When you get into short barrel .308s you lose a significant amount of performance for the payload you are carrying.
The development of the 6.8 and 7x46 had shorter barrels in mind, and thus less performance is lost when you go from 20" down to 16" or 12" than with the .308.
I don't have a ballistics chart on the velocity loss of the .308, but when you get below 16" a lot of the smaller calibers actually equal or surpass the .308 with less recoil, flash, and blast.
Burt Gummer
12-24-09, 17:30
18" barrel should be the absolute shortest length for a .308, IMHO.
Then it really does sound more like a cartridge to compete with the 7.62N than the 5.56N. Similar ballistics and recoil impulse, guestimated weight and size closer to the 7.62N end than the 5.56N end, etc. I agree that adopting a larger caliber than the 5.56x45 is a good idea, but adopting something only a little smaller than the .308? I really like what the 6mm AR and 6mm AR Turbo bring to the table, but we're only talking 3k-4k barrel life out of SS barrels, maybe twice that out of chrome-lined barrels (definitely unsat).
That 2003 chart also seems to indicate that recoil impulse is pretty important for getting rounds on target (supporting the fellow I quoted/linked-to earlier). It should also be pointed out that this is before the adjustments in how our Coalition troops are being fought in Afghanistan (longer and longer ranges, staying just inside mortar and RPG range but out of rifle range, etc.); I wonder if the curve would be the same now as it was in 2003.
Does the 7x46mm have a unique case head size? If so I've an idea (http://www.snipercentral.com/forums/viewtopic.php?t=28826) I've been tossing around that I'd like to compare it to, just for shits and giggles.
-B
this is the first I've seen discussion on a 6mmAR cartridge. I'm assuming this is on the standard 5.56 case? why would barrel life be decreased?
is there any followup material that you can point me to?
ETA: ah, never mind, I found it.
http://www.6mmar.com/
quite a bit different than simply loading the 5.56 case with a 6mm bullet.
From: https://www.m4carbine.net/showthread.php?t=19936
Keep in mind a lot of bullet diameters were tested as part of the SPC development, including 6 mm and 6.5 mm ones:
In general, 6 mm ones did poorly against intermediate barriers compared to larger projectiles; 6.5 mm ones did not upset as rapidly or prove as destructive as the 6.8 mm and 7 mm ones.
so what is the short version of why the 6.8 was chosen over 7mm in the SPC?
Heavy Metal
12-24-09, 18:47
so what is the short version of why the 6.8 was chosen over 7mm in the SPC?
Because the 6.8 will work in the M-4 Platform with a mag, bolt and barrel change. The 7mm requires a total re-design.
Because the 6.8 will work in the M-4 Platform with a mag, bolt and barrel change. The 7mm requires a total re-design.
are we talking about the same thing? you must be thinking I'm asking about the 7x46.
Doc Roberts posted:
Keep in mind a lot of bullet diameters were tested as part of the SPC development, including 6 mm and 6.5 mm ones...
In general, 6 mm ones did poorly against intermediate barriers compared to larger projectiles; 6.5 mm ones did not upset as rapidly or prove as destructive as the 6.8 mm and 7 mm ones.
my reading of this is different calibers were tried on the same SPC case. would this require a different platform?
sorry for the confusion and mini-hijack of the thread...
Negative ra2bach, 6mm AR and the Turbo version are both necked down Grendel cases. More on them can be found at 6mmAR.com (http://www.6mmar.com/).
The 7mm in the SPC case would limit bullet selection to only the lightest, least efficient bullets available. You can do more with a 6.Xmm out of an SPC case than a 7mm. Of course, I'd experiment with backing the shoulder up a bit, sharpen it to 30-40 degrees to keep the same capacity, and trim the now-longer neck to allow for longer bullets... but that's just me. If I am correct in my assumption that the SPC case was a constant and length wasn't played with, that would explain why the 6.8mm was selected.
To restate, my main concern about the 7x46 is that it seems too much like a .308, or on the lighter end of the spectrum of cartridges dubbed "battle rifle" calibers. This is purely my inferring from what has been shared about the round, fully understanding that not all of the information is public. Whether due to my lack of experience in the areas of small arms and/or soldiering, this looks a lot like the pendulum is swinging a little too far in the search for something to replace the 5.56N with.
-B
Negative ra2bach, 6mm AR and the Turbo version are both necked down Grendel cases. More on them can be found at 6mmAR.com (http://www.6mmar.com/).
The 7mm in the SPC case would limit bullet selection to only the lightest, least efficient bullets available. You can do more with a 6.Xmm out of an SPC case than a 7mm. Of course, I'd experiment with backing the shoulder up a bit, sharpen it to 30-40 degrees to keep the same capacity, and trim the now-longer neck to allow for longer bullets... but that's just me. If I am correct in my assumption that the SPC case was a constant and length wasn't played with, that would explain why the 6.8mm was selected.
-B
yes, I see. I got that 6mmAR link after I posted and went back and edited my original question. impressive.
at first, I was under the impression that it might be similar to the 7TCU but using a 6mm projectile. this would still load and chamber from standard 5.56 mags with just a barrel change but with the advantage of possibly heavier projectiles while maintaining OAL.
downside would be reduced velocity. I have no idea how this would affect external and terminal ballistics. do you know if this has ever been tried in the AR platform?
thanks for following up with me...
Burt Gummer, none of the 7.62mm loads quoted are going to be Hague compliant.
ra2bach, I would guess the 6.8 gave better velocity/trajectory with the SPC case while the 7mm needed a slightly larger case, hence the development of 7x46mm.
To restate, my main concern about the 7x46 is that it seems too much like a .308, or on the lighter end of the spectrum of cartridges dubbed "battle rifle" calibers. This is purely my inferring from what has been shared about the round, fully understanding that not all of the information is public. Whether due to my lack of experience in the areas of small arms and/or soldiering, this looks a lot like the pendulum is swinging a little too far in the search for something to replace the 5.56N with.
-B
I agree. the 7x46 seems an attempt to affect the heavy end of the spectrum and because of it's requirement of a larger receiver than the 5.56, not suitable in the role of the light. but what do I know...
there are obviously way-smarter people than I looking seriously at this issue but from the comfort of my armchair, I don't see how we could ever get one cartridge to do the job that is currently being done by several.
common sense would dictate that we keep the platforms we have and increase the lethality of the "light" platform, and increase the efficiency of the "heavy" at the smallest cost of development and deployment.
downside would be reduced velocity. I have no idea how this would affect external and terminal ballistics. do you know if this has ever been tried in the AR platform?
Which, the 7TCU? Beats me. I think you'd be wasting a lot trying to put a 7mm-.223 into an AR15. Not enough capacity to push that 7mm very well for very far, and mag length limits you to the lighter bullets (same problem as I mentioned using 7mm out of a necked-up but otherwise unmodified SPC case). 7mm out of AR10 is a lot more feasible.
I just had the random thought of what a 6.5 SPC or a 6.8 Grendel might be capable of. :eek: I may have to explore this more...
-B
The fact that the 5.56 is less "effective" then the 7.62NATO, should not come as a surprise to anyone.
It is an assault rifle cartridge, and by definition is a compromise.
The decision to adopt it, was not made in some vacum, or fantasy, where it was believed to be the full equal of the .30cal "battle" cartridges. Perhaps, it was overstated or over estimated, but I don't think anyone ever did, or does think they are equal.
There is more driving the train then pure "terminal effectiveness". The 5.56 was meant to give the soldier, a cartridge that was effective enough, in the most common engagement scenarios and ranges believed to be encountered. While delivering a lighter weapon, higher capacity, lighter ammo, that uses less resources to produce and ship.
Keep in mind, the big military, See's small arms, as relatively inconsequential. Seeing things like, indirect and close air, air superiority, and of course logistics, as far more important. I know this sux, for us Infantry types, but there it is. Like it or not, the M1, did not win WW2.
One could easily compare the 7.62 NATO to various hunting calibres, .338, 0r .50BMG for that matter, and make the 7.62 appear weak, but that would not be a reasonable comparison, would it. Nor does comparing an assault rifle cartridge with a "battle rifle" cartridge.
Besides, I've talked to to many troops, from VN era, to the current conflict, who have zero issue with the 5.56, for me to discount it entirely.
As a young 11B, I too thought I wanted an M14 and the 7.62, but that was all based on reading Guns and Ammo and what my friends dad told me. After carrying the M16fow weapons, for a while, I began to realize the benefits of the system, now, over 20 years later, and carrying some sort of M16, for the majority of it, I have no issues with it.
The idea of issuing different weapons of differing calibres to various troops based on the mission, I think, is less then ideal also. It would needlessly complicate logistics & training.
In the end, lets not loose sight of why we went to an assault rifle in the first place, weapon and calibre.
So, while a replacement for the 5.56 may be warranted,we should be careful, as noted above, to not let the pendulum swing to far in the opposite direction.
Bob
Thomas M-4
12-24-09, 20:24
ra2bach WOA makes a 6mm from a necked down 6.8spc case called the the 6mmWOA.
I have enjoyed reading this thread . Has much has I would like to see 7x46mm battle rifle has BAC pointed out I don't see any army going back to a battle rifle. The 6.8 spc would be the ideal choice maybe one day :rolleyes:
May be DocGKR could answer this I have read that the SSA 97 grain AP can defeat IV body armor. I remember reading it in the 6.8spc forum I tried finding the thread last night with no luck maybe some one can chime in on confirming or denying this.
ra2bach WOA makes a 6mm from a necked down 6.8spc case called the the 6mmWOA.
Yup. It's already won a few competitions too (suggesting to me that my interest in wildcatting the SPC case has some merit). A fellow going by the user name "Constructor" on 68forums is also making a 6x41, necking down the SPC case to 6mm and shortening it by a couple mm to fit slightly longer 95-100gr bullets. I'm wondering what doing something similar for 6.5 bullets might do to help make a more efficient bullet that can still defeat auto glass. Alternatively, I'm going to try to find some free ballistic software to see what a 6.8mm out of a Grendel case may be capable of (hopefully allowing slightly longer 6.8mm bullets with a little more juice behind them).
The Grendel and SPC cases are both great starting points, I think, to find a viable replacement for the 5.56 NATO that keeps most of the desirable "assault rifle" characteristics while giving our particular assault rifle a little more to work with but with minimal system changes (ideally just bolts, barrels, and magazines). And I kinda like wildcats. :D
Thanks for your input, Bob. It's always good hearing from the perspective of the folks that would actually be using these systems.
-B
ra2bach, I would guess the 6.8 gave better velocity/trajectory with the SPC case while the 7mm needed a slightly larger case, hence the development of 7x46mm.
it's possible... I was responding to the the Picture that Doc GKR posted which showed the different calibers in the same SPC case.
tracking the discussion when the round was originally introduced led me to believe that 7MM bullets could be used but were not optimal vs the 6.8 due to bullets available at the time.
Which, the 7TCU? Beats me. I think you'd be wasting a lot trying to put a 7mm-.223 into an AR15. Not enough capacity to push that 7mm very well for very far, and mag length limits you to the lighter bullets (same problem as I mentioned using 7mm out of a necked-up but otherwise unmodified SPC case). 7mm out of AR10 is a lot more feasible.
I just had the random thought of what a 6.5 SPC or a 6.8 Grendel might be capable of. :eek: I may have to explore this more...
-B
no, I was asking about the 6mm-.223 or 6x45. some loading charts are claiming 2700+fps with a 90 grain bullet. fired from the same platform, bolt, and mags that would be a pretty useful improvement over the 5.56.
I don't know what the OAL on this cartridge would be but I can't see it being worse than a 75VLD in 5.56.
no, I was asking about the 6mm-.223 or 6x45.
6mm-.223 has existed for the AR almost as long as the .223 itself. It didn't take long at all for benchrest shooters and wildcatters to want more out of it. It's a proven performer out of AR15s and very accurate, but suffers in the bullet selection department. 85 to 90 grains is about as big as it can get before you eat too much into case capacity. It's good, but advantages over the .223 have diminished with the greater availability of heavy .223 bullets. I somehow doubt that 90 gr bullet is moving at 2700 fps at safe pressures from a 16" AR15 (which it would need to in order to be viable as a replacement for the 5.56x45).
Does anyone know if the SPC case size was a set constant throughout the 6.8 SPC's development?
-B
6mm-.223 has existed for the AR almost as long as the .223 itself. It didn't take long at all for benchrest shooters and wildcatters to want more out of it. It's a proven performer out of AR15s and very accurate, but suffers in the bullet selection department. 85 to 90 grains is about as big as it can get before you eat too much into case capacity. It's good, but advantages over the .223 have diminished with the greater availability of heavy .223 bullets. I somehow doubt that 90 gr bullet is moving at 2700 fps at safe pressures from a 16" AR15 (which it would need to in order to be viable as a replacement for the 5.56x45).
Does anyone know if the SPC case size was a set constant throughout the 6.8 SPC's development?
-B
I agree. it's almost certain that the velocity quoted was tested in a bolt action with a barrel longer than 16".
and, due to the larger base diameter, 6MM should be able to easily equal or exceed the velocity of any bullet of the same weight in 5.56mm fired from the same case.
so, I wonder why we have experimentation with longer/heavier bullets in 5.56 when more lethality is desired instead of looking to a slightly larger diameter projectile fired from the same case?
thaks for the reply. I'm enjoying this discussion also...
Does anyone know if the SPC case size was a set constant throughout the 6.8 SPC's development?
-B
that's a good question. my comments were prompted by this pic posted by Doc GKR:
http://i459.photobucket.com/albums/qq319/DocGKR/SPC_trials.jpg
it appears that the cases are all the same with only different size bullets...
This article is the most accurate public account I have encountered discussing the 6.8 mm genesis and appears to answer many of the questions posed regarding early 6.8 mm development: http://demigodllc.com/articles/6.8-mm-spc-cartridge-history-development-hornady-stag-arms-carbine/
For cartridges intended for combat use, you will likely want to avoid sharp shoulder angles...
7.62x51mm definitely remains a viable combat cartridge, especially when fed effective ammunition--the problem remains which modern rifle is reliable, durable, and ergonomic enough to be a viable option on the current battlefield...Mk17 shooting Mk319 seems to have potential, but time will tell.
This article is the most accurate public account I have encountered discussing the 6.8 mm genesis and appears to answer many of the questions posed regarding early 6.8 mm development: http://demigodllc.com/articles/6.8-mm-spc-cartridge-history-development-hornady-stag-arms-carbine/
For cartridges intended for combat use, you will likely want to avoid sharp shoulder angles...
7.62x51mm definitely remains a viable combat cartridge, especially when fed effective ammunition--the problem remains which modern rifle is reliable, durable, and ergonomic enough to be a viable option on the current battlefield...Mk17 shooting Mk319 seems to have potential, but time will tell.
thanks Doc, this is outstanding information.
to the OP, sorry for the hijack of your original subject the 7x46 Murray cartridge...
While an interesting (long!) read, it unfortunately doesn't answer my question about the specifics behind why the SPC case size and shape were chosen. I understand that it's somewhere between a 5.56x45 and 7.62x39 in dimensions; that part makes sense to me. I guess what I'm most curious about is whether body length, shoulder angel, neck length, and overall length were really played with at all during the SPC's development. Shoulder angle is something I hear a lot about but that doesn't seem to be problematic in bolt guns or the AR family of rifles (6mm PPC, 6mm AR, 6.5 Grendel, the various Ackley Improved rounds, etc.). I understand that competition shooting isn't combat, but it's something that at least warrants testing, no?
-B
While an interesting (long!) read, it unfortunately doesn't answer my question about the specifics behind why the SPC case size and shape were chosen. I understand that it's somewhere between a 5.56x45 and 7.62x39 in dimensions; that part makes sense to me. I guess what I'm most curious about is whether body length, shoulder angel, neck length, and overall length were really played with at all during the SPC's development. Shoulder angle is something I hear a lot about but that doesn't seem to be problematic in bolt guns or the AR family of rifles (6mm PPC, 6mm AR, 6.5 Grendel, the various Ackley Improved rounds, etc.). I understand that competition shooting isn't combat, but it's something that at least warrants testing, no?
-B
the way I read the article, the case was chosen because of head size and desire to provide a larger bullet that would fit in the AR platform. any larger head size and it would have required removing more metal from the AR bolt, or using a rebated rim, which they tried but rejected.
OAL length would be decided by magazine length, neck length by caliber and shoulder angle by tried and true. if you look at modern cartridge design, a 30% shoulder is at the beginning of steep with the Ackley Improved 40% angle about at the limit for reliable feeding in a bolt actions. if you look at the military cartridges, the shoulder angle hovers around the 20-26%.
Microalign
02-09-12, 09:29
Interesting caliber. I've always wanting something that was right in between the .308 and 5.56, and this seems to hit the mark.
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