Canadian IVI C77 Ball (our M855) is actually quite accurate even from lot to lot.
I can't recall the exact specifics in the Publication but the maximum required mean spread per 10 shots at 300 meters is very small.
At least the current product is. Not the bad stuff they were pumping out about a decade ago.
The real tragedy of the M855 is it's terrible performance on "medium density game". Because of the design of the projectile, the only way to get it to perform well is to either have a direct hit on a major organ/artery or bone or
if the projectile fragments it can cause severe permanent traumatic wound channels up to 7cm wide. Fragmentation is the primary ideal terminal effect of the 5.56mm military round.
Failure of the projectile fragmenting means the projectile will simply tumble and in all probability pass clean through (failing to hit any major artery, bone or organ obviously). It doesn't have nearly enough mass to do any real damage from temporary cavitation on tumbling. We are soft "elasticy" peoples all in all.
It's velocity must be above 2,700 fps regardless of FMJ projectile to even give it a remote chance of fragmentation however. So out of a 20" classic barrel throwing M855 that puts the most lethal probable range at less than 150 meters.
With a standard M4 14.5" barrel it's less than 45-50 meters! That's not that much distance at all.
And we keep chopping our barrels shorter and shorter to boot making the round ever more useless.
At 11.5" barrel with an M855 it's less than 15 meters!
A good read on the subject in general:
http://www.angelfire.com/art/enchanter/terminal.html
