Well yes, EM rifles like railguns could conceivably launch very small projectiles are rediculous speeds, but the acual level of damage against soft tissue would not be so much (compared to a larger projectile, at slower speeds).
It works well for (theoretical) large-size tank / battleship mounted cannons, that are able to launch smaller ferrite projectiles at insane speeds (mach 3 or above over 25 miles or so...). However, for infantry purposes, launching a small projectile at very high speeds wouldn't do much damage, certainly not more than a regular assault rifle, although it would have long range and excellent accuracy.
The ability to launch somewhat larger than standard size slugs at reasonably fast speed means more damage potential. With a railgun, you'd still see a lot of recoil though. Not so sure about a coilgun (although the ability to accellerate projectiles to high speeds is not quite as good with a coilgun, apparently. Not much evidence of this, since weapon laws prevent construction of coilguns with really high muzzle velocities)
I'm kind of assuming some kind of advanced coilgun, here... Also, the 5.56 was somewhat arbitrary, since I couldn't remember if NATO standard was 5.56 or 7.62 :roll:
However (bottom line), since most of the stuff about EM rifles is theoretical anyway, you could just as easily have a rifle that fires very small projectiles at rediculous speeds (remove the problem about ammo capacity). Also, it occurs to me that the idea about incorporating long recharge times might not be a good idea, since you then basically have a weapon which does exactly the same as the normal sniper rifle - powerful, accurate single shots.
-PsyW
EDIT: Fixed some spelling / grammar.
EDIT2: BTAxis, every time I post you seem to somehow get a post in before me! :roll: