Welcome. Mixing PSA and BCA is probably not a good idea. I have 2 PSA guns and the uppers only fit the PSA lowers. The BCA upper I have fits both DPMS and Bushmaster Lowers. My best guess is the BCG isnt quite in line w/the receiver extension. As well as spring and buffer length problems. I replaced the entire buffer system on the PSA with the Armalite recoil system.
https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01&ReturnURL=/Armalite/Product-Category/AR10-Parts-Accessories&Category=4eeff98b-d9a6-40fd-be6b-ab2e44ec1080