My Rusty xcr also has this same issue. Felt like the mag locked in but wouldn't strip rounds after 4 or 5 shots. Not sure how the mag stayed in that long. Mag arm is as tight as it'll go. Judging by the other xcr I had with me it looks like the arm is out of spec. I haven't had a chance to pull it and measure. SN is very low 11k.
I emailed RA about the mag release. They sent me a video on the fix.
Short answer; Use something non-marring and a hammer to tap/bend the forward end of the arm to engage the mag more. Took me about 30 seconds. Haven't shot it but the mags hold now and drop free
Last edited by navalbeaver; 11-14-2018 at 08:21 AM.