Welcome! I don’t have a whole lot of experience with this platform, but will soon. I’m sure somebody more helpful will come along tonight or tomorrow. It’s my understanding that usually running C-Products or ASC magazines will help a lot. Enhanced firing pins are necessary to reliably run Russian ammo with those hard primers. Most if not all half decent manufacturers realize this now and a complete upper will come with one assembled. If this isn’t the case, it’s a cheap and easy fix. You shouldn’t need a heavy spring with the enhanced firing pin. Standard buffer setup should be fine too. As with any other build (actually more than most of them) YMMV.
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