View Full Version : Reduced utility of .308 in shorter barrels?
dorchester
02-27-10, 14:06
Shorten a .308 barrel enough and the velocity drops to a point where fragmentation/expansion is compromised and muzzle blast/flash can increase to quite high levels. Here's the question: at what point do you stop shortening a 7.62X51 and just go to an already short 7.62X39 rifle? I doubt (but do not know) if a 16 inch .308 will fragment an FMJ style round; perhaps at that point only expanding point rounds should be carried. So here's my REAL question: I see a lot of 16 inch .308 rifles on the market (one of them I own) and yes they are more handy than the full size guns, but... are we just kidding ourselves that we have a more powerful rifle for our pains? Assuming the lack of fragmentation of an FMJ, is the relatively small increase in penetration over 7.62X39 worth all the hassle? Would it be smart to limit 16 inch .308's to Noslers and other good expanding bullet designs only? Since I also have an 18 and 20 inch .308 to use this is more than just a theoretical question. Thanks for any insights folks. Signed, "Too many uppers dude"
Gutshot John
02-27-10, 15:48
At shorter ranges it strikes me that that's not going to be an issue. Certainly you would lose fragmentation velocity sooner/closer but losing it altogether seems questionable.
At longer ranges it probably runs out of gas sooner but shot placement rules. There's a fellow here and on the FALfiles who can speak to it more intelligently than I can but based on his chrono measurements it averaged about 50fps per inch of barrel lost so from 21 to 16 inches you're looking at 250fps if memory serves.
Do you have good numbers on .308 fragmentation/velocity tables? I'd be interested in seeing what it has to say. You seem to be taking it as gospel that fragmentation drops off at a 16" barrel. Not that it doesn't, I just haven't seen the data for that.
All in all it depends on what your requirements are. If you dont' really intend on shooting beyond 100-200 yards the 7.62x39 is a fantastic cartridge. If you want 200-500 yards out of it the 7.62NATO has its virtues.
Shooting 155gr, 168gr or 175gr .308 bullets with better BC's and better SD's will yield better results than a .311 bullet in most cases, even when velocities are similar.
I obviously defer to anything DocGKR might have as data, but when I reviewed this some time ago the 7.62NATO/.308WIN still possessed quite an advantage in energy, velocity, SD, and BD -- even down to 12.5" barrels.
EDIT: For a look at what a slow moving .308 will do, check out the performance of the 300 Whisper/Fireball. The 125gr 2100 fps load mimics a 7.62x39. Now add a lot of case capacity, and a longer and heavier bullet. Sounds like a winner over either the Whisper or 7.62x39.
Burt Gummer
02-28-10, 08:30
With conventional .308 rounds, it is my understanding that it takes an 18" barrel to fully burn the propellant. Shorter than 18" and you increase muzzle flash. With the advent of the Mk 319 Mod 0, where the load is optimized in shorter 16" barrels, compact battle rifles will be much more practical.
I'm hoping this trend in caliber development (Mk 319 Mod 0) will spill over to the civilian/LE side with manufacturers. Maybe Hornady will produce a "short barrel" .308 round with 130 gr AMAX for their TAP line?
Ga Shooter
02-28-10, 09:03
[QUOTE=SHIVAN;585264
I obviously defer to anything DocGKR might have as data, but when I reviewed this some time ago the 7.62NATO/.308WIN still possessed quite an advantage in energy, velocity, SD, and BD -- even down to 12.5" barrels.
.[/QUOTE]
I am currently torn between an precision bolt action and a Larue OBR. Along with my dilema is what barrel length. How much accuracy/power gets lost with shorter semi-autos as compared to longer bolt guns out to 1000 meters? Is there such a thing as "the best" setup? :confused:
Figure out what you need the tool to do.
An AR-10 carbine, HK51, OBR, or SR-25K fits a distinctly different mission requirement than a sniper rifle.
135 and 155 Match Kings (as well as Ball and M993 AP) out of a 16-inch barrel is quite a lot of kinetic energy.
If the shooter wants to use his standard SOPMOD enhancements and doesn't want or need the AK, why use an AK?
With conventional .308 rounds, it is my understanding that it takes an 18" barrel to fully burn the propellant. Shorter than 18" and you increase muzzle flash.
Muzzle flash was significant (think: fireball) from my 16" Ruger Compact with mil ball, import, and some commercial loads until I installed a flash hider. With the flash hider, it is still present but more limited.
With the advent of the Mk 319 Mod 0, where the load is optimized in shorter 16" barrels, compact battle rifles will be much more practical. I'm hoping this trend in caliber development (Mk 319 Mod 0) will spill over to the civilian/LE side with manufacturers. Maybe Hornady will produce a "short barrel" .308 round with 130 gr AMAX for their TAP line?
There are loads coming to the market which will be optimized for short barrels. Right now they are not commercially available.
dorchester
02-28-10, 12:11
I really don't know if a 16 inch .308 FMJ will fragment at even 5 yards, what little I've seen and recall implied something like 2700 fps was needed to fragment an FMJ .308. Muzzle velocity on this barrel is about 2620 fps with German 147 gr surplus ammo, 2550 fps with Portugese and 2700 fps with most commercial 150 gr softpoints. If it's not going to fragment I almost might as well have an AK or VZ-58, unless I use expanding point bullets. That's the conundrum: is a 16 inch .308 giving you what you pay for (in weight, size, muzzle blast, hassle and money)? For now, I'll keep the 20 inch upper on my AR-10, at least until I can find research or test on my own to see if 16 inches will fragment at a reasonable distance downrange. Anybody got the data out there?
While a few specific loads do fragment at higher velocities (generally above 2700 fps), the vast majority of 7.62x51 mm FMJ projectiles do NOT fragment at any normal velocities in barrels 26" and less.
Except for certain mission specific tasks, I prefer .308 rifles with 16-20" barrels--this offers excellent terminal performance with the common early upsetting 130-155 gr projectiles, as well as good accuracy with the 168 & 175 gr loads match loads. The recent KAC SR25 EM and LaRue OBR with 16" barrels are superb examples of this type of rifle.
dorchester
02-28-10, 13:35
Interesting data, thanks for that. It appears that for superior lethality the 7.62X51 is best with HP/SP style bullets in most any reasonable barrel length. It makes me wonder if the reputation of the battle rifles for superior power is mostly a penetration of barricades issue rather than wounding mechanisms.
While barrel length is always a factor in performance with rifle rounds, and I'm sure that 20" and longer barrels really wring the most potential out of 7.62x51 loads, I've heard of several confirmed "engagements" on targets at LONG ranges (including one past 900m) using Mk17s with CQB barrels (13.7") and the newest Long Range ammunition that elements of USSOCOM are getting.
So, once again, I think it's really a question of what your specific application is. For most LE and civilians, I'd think that engagements at or beyond 300m are going to be EXCEEDINGLY rare - so barrel length really shouldn't be a concern. And, while I don't have any studies to prove it, I simply don't think the 7.62x39 is inherently as accurate for shots beyond 100m as the 7.62x51 out of any equivalent barrel length...
Regards,
Kevin
Gutshot John
02-28-10, 16:59
While barrel length is always a factor in performance with rifle rounds, and I'm sure that 20" and longer barrels really wring the most potential out of 7.62x51 loads, I've heard of several confirmed "engagements" on targets at LONG ranges (including one past 900m) using Mk17s with CQB barrels (13.7") and the newest Long Range ammunition that elements of USSOCOM are getting
Could you elucidate further?
dorchester
03-01-10, 09:07
My original question was strictly "Terminal Ballistic" in nature and it remains so. It's hard for me to imagine (in my scenario) using a weapon beyond a 100 yds, much less 900. Like a lot of folks, I wanted something a little more effective than the 5.56. At the time the 6.8 wasn't around and even now, I don't know if it's going to be "fruitful and multiply". Personally, I'm encouraged that my 16 inch upper is as valid a choice as any now that I know that any barrel length will do.
My 16" AR10T carbine clocks 2450fps with Winchester 168gr match ammo. My 24" Remington 700 PSS clocks 2550fps with the same lot. I doubt anyone hit by the slower bullet will notice the difference inside 800 yards. I have not chrono'd ball ammo from the guns.
But.... how loud is it?
:D
dorchester
03-04-10, 14:40
I'm busted...:D
vicious_cb
03-04-10, 21:02
Might be alittle off tangent but what kind of wound channels are to be expected at long range from a .308? Im talking greater than 400 or so yards. Would there be a huge difference in terminal ballistics when shooting 147gr FMJs vs shooting 168gr and 175gr OTMs at long distances?
At long range, terminal performance is the same (bullet goes in, yaws, and exists), accuracy differs greatly....
Dorchester, You may find this article of interest.
http://www.tacticaloperations.com/SWATbarrel/
I think 18" is optimal. My son's LR308B is very accurate.
ReconRanger
03-07-10, 13:31
The only thing better than a 20" 308, is a 18".
308 is a very efficient cartridge and gets most of its velocity from the first 10 inches of the barrel.
While a few specific loads do fragment at higher velocities (generally above 2700 fps), the vast majority of 7.62x51 mm FMJ projectiles do NOT fragment at any normal velocities in barrels 26" and less.
Except for certain mission specific tasks, I prefer .308 rifles with 16-20" barrels--this offers excellent terminal performance with the common early upsetting 130-155 gr projectiles, as well as good accuracy with the 168 & 175 gr loads match loads. The recent KAC SR25 EM and LaRue OBR with 16" barrels are superb examples of this type of rifle.
Doc or anyone who might know more about the subject at hand,
Any idea what the terminal ballistics of the 165gr and 175gr loads mentioned would be like when fired from a 12.5" barrel? Do you have an estimated effective range on such a rifle/ammunition combo? I know it's a pretty broad question, just trying to get an idea here.
With this, the 12.5" HK417 and SCAR H CQC come to mind. The advertisd muzzle velocity for the 12.5" HK417 with 175gr M118LR is 709 m/s (2,326 fps). Would one be able to load such rounds to achieve higher velocity without overpressure issues or is that typically a no no?
Tspeis
Sorry for jumping in late on this one.
I have an HK51 with an 8.3" barrel. I did some un-scientific testing. I shot large 40 gallon water jugs with various rounds to see what would happen. XM193 55gr. 5.56mm rounds would penetrate, on average, 22" and reliably split into two fragments along the canneleure(sp?). 110gr. Hornady TAP .308 would penetrate 20" and completely fragment. I know that its not supposed to matter, but the 5.56mm rounds would cause just a tiny ripple on the water surface while the .308 rounds would actually explode the containers.
Recoil was light from the HK51. Muzzle flash at night with the TAP ammo wasn't bad at all with an HK flash hider. No more than an M14 shooting ball. Surplus ball ammo was a fireball.
"Any idea what the terminal ballistics of the 165gr and 175gr loads mentioned would be like when fired from a 12.5" barrel?"
Yes, some idea.
"Do you have an estimated effective range on such a rifle/ammunition combo? I know it's a pretty broad question, just trying to get an idea here."
It will likely have no fragmentation potential by 200 yards and just yaw over. In general, the 175 gr SMK has better terminal effects when impacting above 2500 fps. Below is a 175 gr SMK hitting at 400m when fired from a 24" M40A1:
http://www.tridentconcepts.com/alumni/Portals/0/NTForums_Attach/143441869254.jpg
The whole reason why loads such as the 155 gr TSWG OTM and 130 gr Mk319 Mod0 were developed is for use in shorter 12-16" barrel 7.62x51mm weapon systems--why would someone choose to use a 175 gr SMK in a .308 SBR when better options are available?
"With this, the 12.5" HK417 and SCAR H CQC come to mind. The advertised muzzle velocity for the 12.5" HK417 with 175gr M118LR is 709 m/s (2,326 fps). Would one be able to load such rounds to achieve higher velocity without overpressure issues or is that typically a no no?"
You would NOT likely be able to load to higher pressures and still have a durable weapon system, not to mention keeping propellant pressures within reasonable levels and stable at environmental extremes.
Doc, do you have by any chance any data on the German 7.62x51 ammo?
This is all I could find:
Bullet design is AB22 whose terminal ballistic performance in tissue is unique from most other 7.62 NATO FMJBT Ball bullet designs. Rather than pitching up 90 degrees, then pitching backwards another 90 degrees and exiting backwards, AB22 pitches up 90 degrees then breaks into two parts at the cannelure, similar in performance to M193 5.56 NATO Ball.
Source: http://www.afte.org/forum/smf1/index.php?topic=1574.msg22903#msg22903
http://i975.photobucket.com/albums/ae234/rkba01/fal/762MENDM111BallPkg.jpg
Yes, some idea.
It will likely have no fragmentation potential by 200 yards and just yaw over. In general, the 175 gr SMK has better terminal effects when impacting above 2500 fps.
The whole reason why loads such as the 155 gr TSWG OTM and 130 gr Mk319 Mod0 were developed is for use in shorter 12-16" barrel 7.62x51mm weapon systems--why would someone choose to use a 175 gr SMK in a .308 SBR when better options are available?
You would NOT likely be able to load to higher pressures and still have a durable weapon system, not to mention keeping propellant pressures within reasonable levels and stable at environmental extremes.
Doc,
Thanks for the info. Please check your PMs when you get a chance.
Tspeis
This might have some useful info: http://www.ar15.com/forums/topic.html?b=3&f=16&t=382340
Wow! It seems not all steel jacket 7.62 NATO ammo is created equal... sadly the germans changed their bullets on purpose, to avoid fragmentation.
DocGKR, what is the reason the DAG ammo fragments at much lower velocities (=extended ranges)? Thinner jackect?
Have you tested this bullet?
What is the bullet weight and velocity (they should comply with the NATO standard)?
What is the performance of this DAG ammo against common intermediate barriers, compared to gilded metal clad bullets?
It seems that bullets like this present a very cheap and simple alternative to enhance terminal ballistics in this caliber, are there any downsides?
Wow! It seems not all steel jacket 7.62 NATO ammo is created equal... sadly the germans changed their bullets on purpose, to avoid fragmentation.
[...]
Do you know this for sure?
Yes, as did several other European nations.
Do you know when? A rough time frame would be fine.
Thanks
-----------------------------------------------------------
Wounding patterns of military rifle bullets by Martin Fackler
http://www.abload.de/thumb/fackler2qol4.jpg (http://www.abload.de/image.php?img=fackler2qol4.jpg)
http://www.abload.de/thumb/fackler1s2t.jpg (http://www.abload.de/image.php?img=fackler1s2t.jpg)
I'm desperately trying to get my hands on the "Deutsches Waffenjournal" report.
I would guess the gel testing and redesign of 7.62x51 NATO bullets with thin steel jackets was undergone in the early '90s... before that, in the '80s, this fragmenting behaviour was well known but not widely understood.
The Danish performed tests in 1992, and changed their AMA bullets in 1995, and the fragmentation threshold was about 2345 fps, pretty low! I think other countries investigated this subject and made changes before the danish.
http://www.springerlink.com/content/g7278h1558141957/
note this comment, typical reasoning for the changes:
"This behaviour is assumed to be due to a lack of strength in the jacket causing it to break at the cannelure when hitting the target at high velocity. The fragments will increase the already sizeable lesions and may leave the body through several separate exit wounds, presenting problems, both for the surgeon treating survivors and for the forensic scientists when defining the direction of the shot. The legality of this and similar bullets in view of the Hague Declaration of 1899 may be questioned, and we feel that the bullet should be redesigned. A programme to this end has been initiated by the Danish state owned ammunition factory."
http://www.springerlink.com/content/q07948p717287257/
There is no indication, in the german army ammunition data sheets, that the bullet design was changed (1992 to 1996).
Unfortunatly i do not have any newer or older data sheets.
Yes, as did several other European nations.
The Bundeswehr released a video last month about a wound ballistics workshop for military and civilian medical personnel on their official youtube channel. At 2:25 Mr. Kneubuehl explains how the german 7.62 x 51 bullet behaves. As the bullet tumbles, it breaks at the cannelure in half and produces two exit wound channels. It's clearly visible in the video. No further details or data (velocity etc.) is mentioned.
http://www.youtube.com/user/Bundeswehr#p/c/2/G9INE9ewRq0
At long range, terminal performance is the same (bullet goes in, yaws, and exists), accuracy differs greatly....
Doc,
I hate to bump a 7 month old thread, but I didn't feel starting a new one would be appropriate.
Am I correct in assuming that terminal performance would be similar or identical, even with different 7.62mm projectile designs and weights, once you get out to longer ranges (600-800m)?
If that's the case, does barrel length play a significant role in wounding potential at long range? From reading the above quote, I'm inclined to believe that even from shorter barrels (12.5"), terminal ballistics would be similar once you reach longer ranges, no matter what barrel length you started with (12.5" to 20").
If I'm mistaken here, please correct me. Thanks.
Tspeis
Terminal performance at longer ranges is going to be quite similar. Starting with a longer barrel/higher velocity will help your external ballistic trajectory and drift, but not terminal ballistics much beyond 300-400.
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