Quoted: Quoted: No small arms bullet is so magical that it will drop a human with one shot every time.  Troops that have that expectation have been playing too many video games. Absolutely - it's a question of percentages. If (to take a more or less hypothetical example) you were given the choice between a rifle which would drop the enemy with a solid body hit 50% of the time or one which would do it 25% of the time, which would you rather have?

The problem, of course, is coming up with those percentages in a scientific manner.

My point was that anectdotal accounts of the 5.56 77 grain bullet not dropping a few bad guys in their tracks is hardly conclusive that the round is innefective, or that some other round would be significantly better.

Quoted: Those US soldiers who scored seven solid body hits on an Iraqi with Mk 262 rounds only to have him kill two of them might disagree with you about the adequacy of any 5.56mm round.

Anecdotal evidence is virtually worthless. I recall reading a report from vietnam where a use Soldier was shot with 17 rnds of .308 (friendly fire, naturally) from an M60 and survived. That doesn't mean that .308 is a worthless POS.

Bullets do funny things. I'm sure we could find plenty of times where a single 5.56 (hell, even a regulard .22) killed someone, or where someone took 10 .30-06 rnds and still managed to do some bad stuff.

That being said, I wonder what a Taliban would say to a 405gr  from my .45-70 Marlin lever action. I've chronoed some handloads at a shade over 1800 fps :)

The question isn't whether a 5.56mm will kill them - as you say, a .22LR will do that - the issue is how reliably will it promptly disable them so they can't shoot back.

Other things being equal, and leaving aside CNS shots, the effectiveness of a military rifle bullet depends on the size of the wounds inflicted. The size of the wounds depends on three factors:

1. Bullet size and weight.

2. Bullet striking velocity.

3. Bullet design: how fast does it tumble, and does it fragment?

The 6.8mm has a bullet which weighs 50% more than the 77 grain Mk 262, and has 50% more frontal area. It also has 75% of the weight of a 7.62mm, and 80% of the frontal area.

The striking velocity of all three bullets would be fairly similar.

The Mk 262 and the 6.8mm normally tumble quickly and fragment out to all normal rifle distances. The 7.62mm tumbles slowly and doesn't fragment at all (unless you get the German ammo).

So to sum up, the damage inflicted by the 6.8mm is likely to be very close to that of the 7.62mm, and around 50% more than the best 5.56mm loading. Sounds to me to be an advantage worth having, without incurring the weight and recoil of the big 7.62mm.

Tony Williams: Military gun and ammunition website and Discussion forum