Glock Model 42 .380 Auto 6 Round Factory Pistol Magazine w/ Extension 1 Pack Black. Only). Note: Glock magazines can be very difficult to load when new. Often the last round will not fit until the magazine has undergone a break-in period. It is recommended that the magazine be loaded with all but the last round and left for a few days to compress the spring. Cycling the magazine from full to empty multiple times can assist in the break-in period. Specifications for Glock Model 42 .380 Auto 6 Round Factory Pistol Magazine w/ Extension: Manufacturer: Glock Gun Make: Glock Gun Model: Glock 42 Caliber: .380 ACP Magazine Capacity: 6 Round Color: Black Fabric/Material: Polymer Package Contents: Glock Model 42 .380 Auto 6 Round Factory Pistol Magazine w/ Extension What firearm models does the manufacturer say Glock Model 42 .380 Auto 6 Round Factory Pistol Magazine w/ Extension is compatible with? The manufacturer suggests that Glock Model 42 .380 Auto 6 Round Factory Pistol Magazine w/ Extension is compatible with Glock 42Glock 33519: Model 42 .380 Auto 6 Round Factory Pistol Magazine w/ Extension 1 Pack Black