"These are Glock factory mags with the polymer followers and the metal interior. They work great, no jams or misfeeds. They will hold 10 rounds but the 10th round was a pain to get in. What I did was put 9 rounds in, let it sit for a few days then load the 10th and let sit. Just like any new product it just needs to be broken in. Over all I will be buying more of these, for the price they're hard to beat, cheapest I could find for a Glock product."