I have had the same issues with my su-22 when I first bought it. It was used, thousands of rounds put through it actually, but it turned out to be the factory mag the rifle came with. It is one of the earlier Black Dog Mags with the recessed sides/tight fit as well. I would have many many failure to feeds as the bolt stripped a round off of the mag it would pretty much just smash the round. Ended up grabbing a few BlackDog Xform mags from the local gunshow as well as a few online and they all work flawlessly. I have shot everything from Federal Bulk Packs, Remington Subsonics, CCI standard velocity to Remington thunderbolts, Aguila High velocity and even winchester Hollowpoints. CCI MINIMAG Roundnose only giving me Failure to feed issues. Could be due to the waxing they throw on them. You may want to check the firing pin to make sure it is not pertruding out of the front of the bolt, not allowing a new round to be picked up all of the way behind the ejector, indicating it is unfortunately snapped as mine had done. As for the casings getting stuck behind the bolt, or on top of the chamber, it seems like it only happens when rapid firing. Maybe casings are bouncing off one another? But all in all not many malfunctions from my Su. Good luck! Hope this has helped!