What should I try to do with a MRA Maverick that's not feeding (crushing cases, light strikes, wont strip a round from a mag).

Tried tons of shit like new mags, ammo, cleaning/disassembly. Even modified mags with little better but same result. MRA is no help - sent it back but they said it's operating fine. I think it's likely an out of spec lower/upper. Thinking of selling it and cutting my loses.