Area 419 Hellfire 2P-Self Timing Brake w/ Adapter 223/6mm 5/8-24223 6mm Good for any bullet caliber up to and including 0. 243 (6mm) ie 223 5. 56 NATO 204 17 cal etc The HELLFIRE 2P Muzzle Brake is designed to provide an optimized brake for Semi Automatic and or hunting weapons systems with barrels of 20 or less. This brake will offer the greatest performance possible while maintaining shooter comfort. Part of the Patent Pending HELLFIRE Modular Brake System The AREA 419 HELLFIRE Self Timing Brake system is not