The Vepr IV RPK rifle has five US parts; hammer, trigger, disconnector, pistol grip and muzzle brake. Technically it needs six since it's a stamped receiver. Now 922r only applies to the builder, not the owner but I do try make sure all my stuff is compliant in case I ever want to sell it or run with original magazines. My thoughts. The piston itself is welded in place in two sections. Now technically if a muzzle device is blind pinned or welded in place onto a barrel, the muzzle device no longer counts as a seperate part for 922r. Now applying that logic, I think that a welded in piston would be the same, no longer a seperate part because just like a muzzle device- it to is welded in place and is now permanently attached to the carrier. It's not like you can just drift out a pin and pull it apart like on a standard piston, this would require drilling out the welds, then breaking the welds to get the piston free. So given this, I think it is safe to assume the same. Maybe some else might chime in with their thoughts on the matter. Simply, I don't see how BATFE could categorize tack welded muzzle devices as not being a separate part and not apply the same logic to pistons.