waht is the difference between the .223 and the xm193 or m885 and what kind of disadvantages does the .223 have against the xm193 or m885 in terms of velocity and stopping power?
The 5.56 leade (distance from bolt face to rifling) is longer than in the 223, meaning the 556 starts crammed against the rifling if chambered in a 223 chamber. There is really no difference in velocity or stopping power between the 223 or the 556 round. The M855 (SS109) is a 62 gr BTFMJ with a penetrator core in it. It is capable of penetrating a steel pot helmet at 600 meters. The M193 is a 55 gr BTFMJ and is really no different from any other 223 round.
neck angles are different/case thickness/primer pocket crimped
I have been reading that alot of soldiers that actually use the 556 in combat are very unhappy with it's performance.
5.56 is loaded to higher pressure than .223
I'm no expert on ammo, especially this 40 year discussion.
The .223 was originally the .222 special and eventually the .223 name stuck. (w/ the AR-15 entry)
Anyways... supposedly safe to shoot .223 in rifles chambered in 5.56, but not ok to shoot 5.56 in a .223 chambered rifle because of the neck and pressures.
My DPMS has .223 - 5.56mm stamped on the lower and they recommend the 5.56 x 45 for it. The .223 shoots just fine.