Interestingly poor reviews on the mag. I don't know what to think about it, mine work really well after enlarging the mag catch, I just cut away some plastic at the top of the opening with a exacto knife until they lock correctly. The last round bolt hold open also works perfectly every time. I've run a lot of rounds through them, I have eight of them and have no regrets.
http://www.midwayusa.com/product/838...-polymer-black