CMMG 10RND EXT FN5.7 FITS 20RD MAGS

Description

The CMMG 57AFD1E is a drop-in extension kit designed for shooters who run FN Gen1 Five-seveN 20-round magazines and want more capacity without permanently modifying their factory hardware. Installation does not alter the original magazine, so you can return it to stock configuration any time.

The kit pairs a polymer magazine body extension with a replacement spring. The extension is contoured to follow the profile of the factory magazine body, so the joined assembly sits flush rather than creating an abrupt step that could interfere with grip or holster fit. The spring is chrome silicon, a material that resists taking a permanent set under sustained compression and holds up to salt and moisture better than standard carbon steel — relevant if your magazines spend time in storage or in the field rather than cycling constantly through the range.

The extension adds 10 rounds to a 20-round FN Gen1 Five-seveN magazine, bringing total capacity to 30 rounds of 5.7x28mm. Because the system relies on the replacement spring to feed the full column reliably, the spring is the functional core of the kit — the polymer body adds length and round count, but proper feed geometry depends on that spring doing its job through the complete stack. The extension is finished in black and is caliber-specific to 5.7x28mm.