I built a 7.62x39 AR and I’m having FTE issues, but only with brass cased ammo. It was initially doing it with steel cased Tula and a new extractor spring solved the issue. I was out shooting today with my son, and we went through a few magazines in it, not one issue with several different steel cases ammo, but put brass cases ammo in it, and every time it’s a FTE. Gas block is not adjustable, but looks fine and buffer spring is standard factory one with a standard carbine buffer. Any ideas to resolve this issue?
