This is the 3rd Generation CMMG 25 round .22LR '22ARC 25R3' Magazine which replaces the Gen 1 grey and Gen 2 Evo magazines.
Clearly styled on the popular Magpul design they work with Magpul magazine holder accessories.
Built from a tough polymer the magazines are fully strippable for cleaning and feature a full length box spring rather than the coil springs of earlier models. Naturally they are fully compatible with CMMG's Bolt Hold Open Actuator (BHOA) system.
The magazine fits all milspec standard AR 15 Magwell's.