Thanks guys. I actually feel comfortable enough th carry it again. It won't shoot 9 mm rat shot, without jamming, but most semiautomatics wont, so I am happy

So when I was ready to throw my r51 in the lake, due to constant jamming due to rounds diving into the loading ramp, I found this site. I found instructions on how to trim the magazines and polished everything. I put the gun back together, but every time I fired it the slide stop would engage and lock it back. As a last resort, I disassembled and reassembled. It racked and shot perfectly. No more jamming. I am happy, but I still can't figure out what was making the slide stop engage. Anyone know what I did wrong?

Looking forward to learning more about my r51 on this site.