There can be variation in the Mecgar magazines. As with anything else. There is a range from okay to nope, that won't work. Get a magazine that's a bit on the large side (but maybe still in spec) and a pistol with a magazine well a bit closer to the small side (but still in spec) and you may have issues.
Four of the 8, or 10 19 round magazines I bought a few years ago would not fit in my modified Pre CZ85. The first 4 were great, the next four I had two that felt like a rubber hammer might be required to get them to fully insert. Those two had no issues in my CZ75 Compacts or my youngest son's CZ75SA. I traded him those two for two he had that worked great in the old Pre B.
Variation. It's a thing.
Also, magazines can "swell." I bought 3 or 4 Mecgar .40 magazines with the +2 bases on them for my CZ75B .40. Fourteen rounds. Great. Not a one of them would insert easily into the new .40 when loaded with 14 rounds. You shoved them in normally, they stopped short of seating/locking in. So you could give them a good smack, or three, on the bottom and they'd fully seat/lock in. When empty, they'd drop right out. Or insert normally back into the mag. well of the pistol.
Download them to 13 rounds and they'd insert/lock in just fine, like normal. I took the +2 bases off of them and used them on some other magazines. Put the standard steel bases on them and they work just like they are supposed to (oh, also had to buy new springs for them as the original springs would barely start to push the follower up enough to fully engage the slide stop in the slide when the magazine was empty.
A bad piece or two is frustrating, but easy to overcome (most of the time). It doesn't make all of the similar made pieces bad, too.
