I have a lot of the "original" C-Products SS mags.
I never had any problems with the 30 round ones.
Many of the 20 round ones had out of dimension feed lips (too wide a gap) which allowed double feeds or spontaneous round dumping.
The body of the mags actually got wider towards the top as if it wasn't properly jigged during the spot welding.
I think I have about a dozen twenties but it took three return and re-ship episodes before they were all functional.
The mags are larger internally than USGI so they require a special follower. A green, black or Magpul will tilt on corner out of the front of the mag.
I have, however, been able to substitute stainless steel CMMG followers.
The stainless mags I have contained chrome silicon springs not stainless.
All this based on the "original" C-Products. Not sure how much of the technology transferred and how much went to ASC. Also not clear who the bad guys were in that split.