Looks over gassed to me.
Is it worse when shooting suppressed?
Have you tried shutting the gas off completely, then opening it one click at a time after each shot?
Gotta find a way to slow that bolt down some.
I agree over gassing can be part of the problem as well. Bolt velocity is rather high as it slams into the bottom of the stroke. Set gas block by shut all the way down and the alternatively fire rounds with one rounds in the magazine. It will not get to the bolt catch and hold it open until enough gas is cycling to give the bolt enough velocity to far enough back in the stroke. Ounce the bolt catches go another 1/2 turn. If you set it up for non suppresses there will be more gas suppressed. If you shoot only suppressed set it up with your can on. If you go between both you will have to find a happy medium. Doing this and changing the ejector spring to an AR15 spring will get you there.
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