Several different studs made for the plastic hand guards.
My ammo of choice is Lake City M193 surplus, .30 cents a round, full power and accurate. You can save about .10 cents a round shooting steel case but it tends to be dirty ammo.
Pmags are OK, some have problems with mag well fit and there are some reports of the Pmags swelling with age causing the mag not to drop free of the mag well. This is not a problem with usgi mag. D&H mags with the current follower are about $9 ea.