Glock Glock 31 Magazine Features The Glock 31 Magazine is built from Glock s proven black polymer shell with a hardened steel insert a construction method that has earned a reputation for reliability across decades of use. Holding 15 rounds of .357 Sig it gives the Glock 31 shooter a full capacity reload that matches the pistol s original factory specification. Because it is a genuine Glock factory part fit feed and function match exactly what came with the pistol from the factory. This makes it a straightforward choice for anyone who does not want to introduce an aftermarket variable into their carry or duty gun. Like all new Glock magazines this one may be difficult to load to full capacity right out of the box. Loading it with all but the last round and allowing a short break in period helps compress the spring for easier future loading. Cycling the magazine from full to empty several times can also speed up that break in process. For sale at GrabAGun this factory magazine is an easy way to add a reliable spare to any Glock 31 setup. Glock Glock 31 Magazine Specifications Manufacturer: Glock Model: Glock 31 Magazine Caliber: .357 Sig Capacity: 15 Rounds Material: Polymer / Hardened Steel Insert Color: Black Available At: GrabAGun