6.8 Info...

[Razorhunter]

Gentlemen,
Can anyone recommend me a good online source that covers the "5.56 vs 6.8" topic???
I guess I should just say that I'm looking for an article/writeup, that simply shows the difference in knockdown power (ft/lbs of energy) between the two rounds at different distances, with different bullets.
I'm not looking to get SUPER technical with this, and I'm not really wanting to start reading about every technical stat that can possibly be. However, as I said, I'd simply like to read a little bit about the differene in ft/lbs of energy between the two rounds, and maybe a little info on the max effective range(s) with different bullets, etc, etc.
What say guys?
Anyone got a simple but effective source of info out there that has covered this topic?? I'm especially not looking for a 50 page long thread, where 90% of its contents turned out to be a bunch of arguing and fighting over which round is the "better" round...
Thanks for any help guys, and if anyone here has any tech info to add, I'd love to hear it.

[jmart]

You'll have to plug in start velocities which are barrel length dependent, but using this on-line ballistics calculator you can figure out drops, energies, just about anything. I'm assuming you are asking with respect to hunting game, but not knowing on what you want to hunt I wouldn't know where to begin discussing this. Regardless, I would limit each cartrdige to deer-sized game at the largest. You can stretch that with 6.8, but not much.

PM Zak Smith, he has first hand experience with 6.8 on game.

[Sid Post]

https://www.m4carbine.net/showthread.php?t=1580

This was a good read that might be helpful.

[Razorhunter]

Thanks guys, I will check the links out. I do actually hunt quite a bit, but I'm mostly a bowhunter. Years of taking game with a rifle just got boring and too easy. Bowhunting is the SHIZ...
However, I'm not really asking for hunting purposes. Just general self defense inquiry. I have always been totally interested in the 6.8, and I would like to find out JUST HOW MUCH MORE stopping power the 6.8 really has???
I would also love to throw in 7.62x51 to the mix, and see how 6.8 compares to this round as well???
This is something I've always wanted to read about, and it would be great to have it explained and laid out in plain english, for a simple, but informative learning process.
As I said, I'm not trying to dive in and start studying this stuff for hours upon hours, and I know there are literally hundreds of variables that come into play, but I'd just like to get a good general idea of how much stopping power each round has, in comparison with one another. Also, how the trajectories of each round differ as well. Again, a general idea here guys. Nothing SUPER scientific that includes changes in humidity, temperature, barometric pressure, etc, etc, etc, etc!
Thanks guys... Anyone else????

[AR15barrels]

Here is a simple set of graphics showing 5.56, 6.8 and 7.62x51, each from a 14.5" barrel.

[Razorhunter]

Randall, (or anyone else),


1. What are the numbers located inside the square boxes representing?
For instance, outside of the 5.56 graph, it shows "1376.19" -and- "860". In 6.8 graph, there is only one, that says "274.09" -and finally, in 7.62, it shows: "566.26", "2600.00" and "2400".
What in the HELL are those numbers in the seperate boxes????


2. What does "Peak to LOS" mean?

3. What does "Zero Range" mean?

4. What does "point blank max" mean????

I can read the charts, and the specific ft/lbs of energy at certain distances, but I don't understand the numbers in the seperate boxes, nor do I understand the unique phrases in questions 2-4 above...
Thanks for the help, and THANKS for posting the KICK ASS charts! Those were JUST what I was looking for!
Too bad you didn't have them made up for 16" bbl 5.56/6.8, and 20" bbl 7.62...
STILL, GREAT INFO!!!!

[DocGKR]

Paul Cataldo,

Why the focus on kinetic energy? The amount of kinetic energy "deposited" or momentum transferred to a body by a projectile is not directly proportional to the amount of tissue damaged and is not a measure of wounding power. Wounds of vastly differing severity can be inflicted by bullets of identical kinetic energy and momentum; for example 7.62x51 mm M80 ball vs. Hornady 155 gr OTM or 7.62x39 mm M43 ball vs. Win 123 gr JSP. What the bullet does in the body--whether it yaws, deforms, or fragments, how deeply it penetrates, and what tissue it passes through is what determines wound severity, not kinetic energy or momentum.

Anybody who has seen the actual data from some 10,000 test shots collected by the JSWB-IPT at 3-10m, 100m, and 300m distances knows that the clear and unequivocal best performing cartridge in the JSWB-IPT analysis was 6.8 mm. This was again validated by other recent military and law enforcement agency testing—all of which repeatedly have demonstrated that 6.8 mm offers the best terminal performance of ALL assault rifle calibers tested to date.



The JSWB-IPT remarked that: “The 6.8 mm projectile had a near optimal balance of MASS, VELOCITY, and CONFIGURATION to maintain its effectiveness, even at a lower impact velocity.” In addition, it declared that, “The 6.8 mm performance observed in this test suggests that an intermediate caliber is the answer to the trade-off balance issue.” The JSWB-IPT report also wrote: “The best performing systems emphasizing tissue damage, on the average, in this study were of larger caliber than 5.56 mm.”

6.8 mm 115 gr Horn OTM fired from 12" barrel at 100 yards:



Compared to 5.56 mm, 6.8 mm is dramatically more effective at retaining adequate terminal performance after first penetrating intermediate barriers.



6.8 mm offers very good accuracy—recent testing using sub 16” barrel carbines had SSA 115 gr OTM ammo demonstrating 5 shot groups a bit under 1” at 100 yards; for that matter, the BH 115 gr OTM was equally impressive, with 5 shot groups a touch over 2” at 200 yards.

Even after recent extensive testing with tens of thousands of rounds fired, no 6.8 mm bolts broke; of course these are all in quality weapons and not from bottom feeder vendors or civilian Frankenguns of dubious origin.

[DocGKR]

Remember that 6.8mm is an assault rifle cartridge, not a full power rifle cartridge. And just like with the original 7.92x33 mm MP43/StG44, modern engagement scenarios with carbines are still primarily 300m and under, with rare shots out to 500 or so...given this reality, 2600 f/s +/- 50 fps is a reasonable velocity for 110-115 gr projectiles fired from 16" barrels.

Something like a 1/12 is probably going to end-up being the best twist rate for 16" 6.8mm barrels shooting bullet weights up to around 115 gr.

Avoid CP mags--to date, these are NOT proving reliable enough for serious use; the PRI and Barret mags seem to be working well.

[jmart]

Randall, (or anyone else),


1. What are the numbers located inside the square boxes representing?
For instance, outside of the 5.56 graph, it shows "1376.19" -and- "860". In 6.8 graph, there is only one, that says "274.09" -and finally, in 7.62, it shows: "566.26", "2600.00" and "2400".
What in the HELL are those numbers in the seperate boxes????

Not sure.

2. What does "Peak to LOS" mean?

Zero range is 100 yards. The Peak to LOS refers to the yardage at which the peak of the trajectory occurs.

3. What does "Zero Range" mean?

Where the weapon's zeroed. In these instances, 100 yards.

4. What does "point blank max" mean????

The max range at which the the impact falls within a given circle's radius. I'm not sure if Randall's using his 100 yard zero range and then using his "Peak to LOS" value to eatblish the radius, he would then figure out at what distance beyond 100 yards the bullet would fall the same distance below the LOS. Looking at his data I'm not sure if he's using a 100 yard zero though when calculating his Max Point Blank range, nor am I sure what radius he's using (unless he's using the Peak to LOS value as his radius).

To give you a more practical example, for big game hunting rifles shooting a high velocity, flat cartridge, they might establish a 6" diameter circle (3" radius) as the target zone. In this instance the ballistic calcualtors will tell you to zero at 273.6 yards and your max point blank range will extend to 327.4 yards. What this means is your bullet will strike no higher than 3" above or below your aimpoint at any distance from the muzzle out to 327.4 yards. It's a way for a hunter to have to avoid using holdovers -- just hold center of mass and your bullet srike should be within + 3" of your aimpoint. (The above numbers are ficticious in nature, and were used just to illustarte the concept).

I can read the charts, and the specific ft/lbs of energy at certain distances, but I don't understand the numbers in the seperate boxes, ....

Nor do I.

[AR15barrels]

1. What are the numbers located inside the square boxes representing?

Too bad you didn't have them made up for 16" bbl 5.56/6.8, and 20" bbl 7.62.

I made those real quick using quicktarget.

Ignore the square boxes.
When you are using quicktarget, those square boxes show you where your cursor is at on the graph.
This is a tool to allow you more precision in reading the graph.
It just happened that when I did the screen capture on a couple of those, that I accidentally had the cursor over the graph.
Note that there are no boxes on one of the graphs, this means that the cursor was not over the graph.

I chose 14.5" as a barrel length across-the-board to make a more fair comparison.
If I had used 14.5" for 223, 16" for the 6.8 and 20" for the 7.62x51, then someone else would be screaming that I was purposefully biasing the results towards the 7.62x51.
Using the same barrel length, it's plain to see that the 7.62x51 does not need any help being the winner.

2. What does "Peak to LOS" mean?

3. What does "Zero Range" mean?

4. What does "point blank max" mean????

These are dropped-in by quicktarget as well.
Even though we are not looking at the projectile's drop, quicktarget always lays it into the graph.
These were indeed based on a 100yd zero as suggested already.
Point blank was based on a 6" circle so no more than 3" above/below the line of sight.