5.56 Nato 75 gr InterLock® HD SBR? Black is designed specifically for 10.5″-11.5″ SBR?s by using proprietary propellant technology and a bullet designed with technology from industry leading Critical Duty® FlexLock® bullets. This round provides exceptional ammunition performance in SBR?s suppressed or unsuppressed with virtually no flash or residue dramatically reduced sound signature will not foul or overheat suppressors uniform velocity and accuracy and provides controllable rate of fire in automatic platforms. Designed to meet the requirements of the FBI protocol this round is the optimum choice for 10.5″-11.5″ barreled 5.56 rifles.