7.62x25 is really inexpensive, accurate and performs much better out of longer barrels (ever seen the fireball at the muzzle of a tok?).
There's also a pretty good chance that Joe knows some people who have access to very large quantities of that ammunition. Actually I'm surprised he hasn't built a 7.62x39 upper, the design work is already done (by Colt in the '80's).


















































