I just heard a very shirt story where a pretty well known Ex navr seal with a tv shiw stated the 6.8 round "carries twice knockdown power of the 5.56".
Is this anywhere near true???

<This is not GD. Comment removed - Z>

Federal Am Eagle advertises 1827 ft lbs out of 6.8 fmj. So...maybe 40-50% more depending on what rounds you compare. No where near twice as hard. I'm not sure what the 100 ballistics are though. It could be true.

Anyone using the term "knock down power" is ignorant of ballistics. Mr. Newton proves it. Physics rules. Any bullet that can "knock a man down" at impact would also knock the shooter down. Google the guy wearing a vest who gets shot with the 308 point blank while standing on one foot and doesn't even wobble to illustrate the principle.

However, increased terminal affect can be realized with a larger caliber. But once adequate penetration is realized, bullet design is much more important than caliber. For example, a 6.8 FMJ will be less effective than a 5.56 with a Barnes TSX. But even with that said, shot placement is paramount. The only way to physiologically knock some one down with a shot, is a hit to the central nervous system (brain/spine,etc); and caliber won't make a difference here. Now if someone drops after being shot anywhere else, that can be attributed to psychological factors. Even with a hit that explodes the heart, there is still enough residual blood in the brain to function for 7-10 seconds. If you have ever hunted deer, you have probably witnessed this phenomenon.

So to answer your question does the 6.8 have twice the knock down power of a 556? No. Is it more terminally effective than 556? With equal bullet types, likely due to a slightly larger wound channel that it can create because of the larger caliber. But all this talk is in reference to human targets. If we start talking big game hunting, then we will have to discuss other factors, primarily penetration due to more momentum of the heavier projectile in the 6.8 giving it an advantage over 5.56.

on avg it's got 40% more energy and that's with shorter barrels

great round and superb for hunting

Agreed.... the 6.8 can fire OTM bullets are proven to perform better in similar tests between the .224 bullets and .270 bullets.....I feel the 6.8 was designed to be a anti personal round from the get go... ( Unlike the jack of all trades 5.56 )..... but the .224 bullets have over the last few years has improved quite a bit, enough that they are pretty dang good performers.

Good enough performers that a wholesale upgrade by the military would be kind of needless.

But......If I could have a unlimited free ammo supply of my choice... I would swap over quite a few rifles for the 6.8....the 100yd to 300yd rifles would go now...... just not the 400yd + rifles

6.8 hits harder for sure. The cheap gold dot rounds are great. Its a good all around cartridge that does very well out of shorter barrels. If it cost 40cents a round I would shoot it exclusively.

Great replies,  Thanks for the information.  Would the 6.8 be a better round for a short barrel rifle?

Yes, if you are talking about terminal performance.  The 6.8 is very efficient and you don't gain much as far as velocity with increased barrel length.  Remember that the 6.8 shows just about ideal FBI specifications for SD ammo and they preform better then 556 (for the most part) through barriers.  There are some 5.56 exceptions but they are mainly high dollar ammo that you may have a few mags of or hard to find ammo.  The 6.8 has most of the loads for it exceed 5.56 performance.

I've never shot a human but I have shot alot of deer and my 6.8 seems to take deer down better then my 30-06 and 308's ever did.  I have had several (most) DRT shots on deer with the 6.8 and nosler AB's, even when shot placement has been behind the front shoulder.  The majority of my 30-06/308 kills ran off anywhere from 50-100 yards when shot through the front shoulders.  The 6.8 is lighter, seems to work just as well if not better then the 30 calibers, and has less recoil.

Also, one poster said if 6.8 was 40 cents a round, he would switch over.  Frankly, it costs less then .40 cents.  Recently, Mass ammo had 6.8 federal gold dots for $115 per 250 rds in an ammo can for .46 cents a round.  Figure that with shipping it may just to 52 cents per round.  Pick the brass up and sell for 25-30 cents a round and you have a net cost of around 22-27 cents per round.  That folks is 5.56 prices or even less, figuring doing the same thing with the 5.56 brass, that you'll get 3-5 cents each for.  They are out of stock right now but PSA has deals in the recent past for FMJ's around .50 cents each.  http://massammo.com/federal-equivalent-6-8mm-spc-90gr-sp-250rd-ammo-can-flat-rate-shipping.html

That's really where 6.8 outshines the 5.56.

6.8 spanks the "Queef Out" every day!!!!

Its a great round if it was a little bit cheaper, I'd never shoot 5.56.

2700 FPS in an 11" 6.8 with a 95 TTSX FTW, 6.8 is a great round for hunting.

223/5.56 is a great round too, each has its place. It's America, shoot what you like!

OP, do you handload? This is where the 6.8 reallyy shines...