I wouldn’t be surprised if you’re running into buffer weight and buffer spring issues trying to run three drastically different uppers on the same lower. I’m guessing you’ve got a carbine length collapsible stock on it also that’s compounding the problem. Rifle length buffers and springs are less sensitive to cartridge changes and/or changes in projectile weights.
Good luck with it. Firearm issues that aren’t easily solved are really frustrating. Maybe reach out to Gundoc, he would know.
