I assume you've tried other mags and all kinds of ammo.
I'd look at the breech face and polish and smooth the part that pushes the shell out of the mag if it looks rough. Some are so bad you can see brass imbeded in the cracks and crevaces. I'd also Flitz, polish and wax the ramp, chamber, breech face, etc. After all that, try a Wolf mag spring.
Good luck, post pics and let us know what's what. My PCR has been 100%