GLOCK 31 Gen4 The GLOCK 31 Gen4, in 357 SIG, is the optimal solution for those seeking high muzzle velocity and superior precision in a reliable, yet lightweight, pistol with large magazine capacity. The Modular back strap system makes it possible to instantly customize its grip to accommodate any hand size. The reversible magazine catch makes it ideal for left and right-handed shooters. Mfg: Glock