The technical reason for not using 5.56 in .223 is the neck can get pinched
in the throat and therefore pinch the bullet, spiking pressures way above
specs for the military round. Winchester has a good article on it if I remember
correctly. has a good diagram of all the various chambers.
The wylde that rra and other builders use safely shoots both.

Edited by bigwheeler (01/28/09 02:07 PM)