It’s only a five rounder, but it would seem other people are getting the idea. In our project to make a 30 round magazine for an M11 submachine gun, we found that the ABS plastic the Makerbot uses to be a bit too flexible for a 30 round magazine. At some point, Jason and I will get around to test firing the design we worked on. But this is pretty neat, considering this 5 round AR mag uses a plastic spring also made on the 3D printer. Our magazine used a metal spring that was from a broken magazine.