These are actually supposed to be 12 round magazines. but Smith and Wesson is in Massachusetts which is forcing them to go to 10 round magazines.
Since the 9c will accept the full size 17 round magazine I bought one of them. Disassembling the 2 clips I found that the spring and follower in the 10 round clip is exactly the same size as the one that's in the 17 round clip. No wonder you can't get 10 rounds in the clip! So I cut the spring down to where it's commensurate with the size of the clip.
You may say it's illegal to modify the spring, but I say it's unconstitutional for Massachusetts to arbitrarily limit the size of the clip. Besides, I live in Ohio where the 12 round clip is legal so Massachusetts can kiss my ***.
It's still hard, but now at least possible to get the 10th round in the clip. I suspect if I cut the follower down it would be easier. Maybe even possible to get 12 rounds in the clip, but I've got the 17 round clip anyway so what the hell.
Smith and Wesson needs to get smart like some of the other gun manufacturers and move out of cukoo land to a state like Tennessee or Texas.