I made a bmg mag and 1 single bullet.you have to print 4 bullet for mag with special bottom blocker (Gadget_Empty.stl and Gadget_Empty2.stl have it)

USE GLUE to stick bullets in your mag, if you want use it like a keychain (you know why, to sit perfectly in mag without slack).You can use it like a keychain, fun toy, i.e

Don't forget like my model after download.Happy Printing !