I cannot find factory replacement magazines for my CZ 83. I do however have one, I am pretty sure is a factory mag. That magazine works flawlessly and does not have a visible seam. The brand new faulty magazines have a welded seam that has been ground opposite the round indicator holes. I disassembled both magazines and compared each part. These were my observations that were possibly causing FTF?s (failure to feed):
The plastic follower has a hole in it to allow it to connect it to the spring. The the factory drilled the wrong position of the hole causing the spring to protrude outside of the follower body making it scrape the interior of the magazine as it travel up as rounds are spent causing drag. The square hole that was punched for the magazine lock has caused the metal to slightly protrude into the wall of the magazine. You can feel this with your finger. You cannot feel this in the factory magazine. As the spring scrapes it?s way along the magazine wall as rounds are fed, it gets hung up on the protruding metal around the magazine stop (square) hole. This causes the FTF.
Solution: take the follower and while using a dremel carefully enlarge the hole for the spring in an egg shape allowing the spring to ride next to the follower and away from the magazine wall. Using a bastard file, file the protruding metal inside the magazine at the square hole so the follower can travel smoothly.
After doing this to 3 magazines they are working fine. Although I had to file one a couple more times. Hope it works for you if you are having these issues.