Check your extractor and see if there are any obvious issues with it. If not pull the fore grip off and look at the ring before the piston assembly. They should have cuts in them. The cuts will likely be offset from each other. Try lining the slots up or increasing the spacing between them.
I do that a time ago but have the same issued the only thing I did was I put a heavy amount of grease around the piston also in the chamber and shoot fine but I hate that amount of grease on my gun any suggestion?