The AAC BlackOut Flash Hider for 51T mounts is an extremely efficient design that effectively eliminates muzzle flash, even on short barrels. The open-end, 3-prong design of the BlackOut is inherently stronger than 4-prong units and is not subject to the wear and erosion commonly encountered with closed-end designs. All of AAC’s BlackOut flash hiders are machined from high strength aerospace steel alloy and coated in a hard, durable, corrosion resistant SCARmor finish. Rocksett Included