The PMAG 20 300 B GEN M3 AR-15 Magazine is a dedicated for rifles chambered in 300 Blackout. 

Optimized for 300 AAC Blackout, the PMAG 20 300 B features a distinct rib design and smoother upper texture to set them apart from other PMAGs for quick visual and tactile identification. This AR mag is easy to disassemble and clean for regular maintenance and won't fail you in the field. While standard AR-15 magazines may be used for this cartridge, the potential danger exists to chamber and fire a 300 Blackout round in a 5.56 NATO chamber with catastrophic results.

Features:

20 Rounds
Dedicated 300 Blackout magazine
Impact and crush resistant polymer construction
Optimized internal geometry for 300 BLK
Anti-tilt, self-lubricating follower
Long life USGI-SPEC stainless steel spring
Over-travel insertion stop
Distinct rib design and smoother upper texture for easy identification
Aggressive front and rear texture