I don't know if you've saw the thread on My American Classic II
but I had the same problem any time the mag was loaded with 8 rds, the top cartridge (or two) would nose dive into the feed ramp at too low of a spot for it to feed, and after the first two rounds it would still occasionally do the same thing.
Anyway, I picked up a Chip McCormick magazine and had the same problem. CA357 put me onto Tripp Cobra Mags
and with a little searching I found that Cane REALLY recommends them and got JD to do a review on them. I ordered one and it ran 6 mags through flawlessly!
I haven't gotten a chance to run any more through it, but I know that it ran the 6 mags without a flaw, during which time I tried the CMC mag 3 more times and it nose dived every time. The ACT mag nose dived about 50%+ of the time.
I saw in my research before buying the gun that this is a problem, and some people have gotten it fixed by using better mags (like I think I did), at least one person fixed it by polishing (re-angeling) the feed ramp), but no one I've seen has gotten it fixed by sending it back for repair. They just send it back with the same problem.
Here's a link to JD and Canes review... Tripp's Cobra magazine Test