The feeding is a little weird, but I don't think it's fully because of the magazine, keep in mind the universal firearms company was not one held in high regard at the time that they made these carbines. Also, this is not one of the original magazines, this is a conversion done after the fact at some point, I have no idea when. The original magazines were something like 4 or 5 rounds, made partially of plastic as I understand, but are extremely rare today. Luckily, you can convert 30 round M1 magazines to 10 round 44 magnum magazines, apparently with some relative ease.
When I got this gun, it would only reliably feed maybe 3 or so rounds per magazine. The others would lock up the action, or otherwise just get stuck. With the recent tests I did, 80% of the feeding went correctly, with only 2 or 3 rounds having issues, 2 of which were corrected by pulling the pump back a fraction before pushing it home again, and one that I accidentally ejected while trying that action.