Smoothly press the magazine straight upward into the magazine well until the magazine catch snaps into place. Pull down on the magazine slightly to make sure that it is caught by the magazine catch. Excessive pressure can force the magazine past the magazine catch. Most commercial metal magazines with blue finish or pressed latch plates require replacement of the shell. ArmaLite sells 20 round magazines when available.
Conversion kits are available to allow customers to convert their own magazines.
Due to design constraints resulting from 1994 Crime Bill, the cartridges in a fully loaded magazine are tightly compressed. Magazines for those same rifles will not work in the current AR-10B series rifles. Disassemble the magazine carefully to avoid losing the spring-loaded Bolt Catch Trip in the Follower. Wipe clean and dry with a cloth soaked with a good bore cleaner. Make sure that the front and rear of the magazine shell are smooth.