I'm sorry to hear about the feeding problem with your M597. Out of the many thousands of rounds that I've fired through the two .22LR ones that I have, I don't think that I've ever had a feeding malfunction. And I've put some severely underloaded stuff through them too, like some Win. Dynapoint that clocks at 1015 fps (and it's supposed to be hi-velocity stuff too).
I've never shot any exposed lead ammo in these guns, only copper plated bullet stuff. I also purchased a bunch of extra mags when I bought the guns, but, to the best of my ability to remember, I think that I've only used the mags that came in the guns. According to what I've read about the M597, I think that some of the initial batch of mags suffered from splits along the glue/heat fusion lines. Most sources say that the splitting mags problem was quickly fixed by Remington. I haven't had any problem with that...
I clean my guns every time that I shoot them, which probably contributes to my good luck with them. I don't think that I've put over 300rds through one at one sitting before cleaning...
I also have a M597M in .22WMR, which I've also had good luck with so far, although I've only put a little over 150rds through it (which isn't much of a test).
I hope that you can find the feeding problem with yours, jcarey.
(And I agree, the mag looks and feels pretty flimsy... But it's worked for me so far).