Bulletproof designed and extensively tested by shooters for shooters, the Tactical Trigger Unit has raised the bar for drop-in AR triggers. The TTU is a single-stage trigger unit that is easily user installed in any AR pattern rifle in less than 1 minute. Wilson Combat engineering enables a durable, 4 lb., ultra-crisp trigger pull without any fine tuning or adjustment. Reduced, positive trigger reset guarantees a quick follow up shot on target. The unique hammer geometry enhances reliable ignition with military and surplus ammunition of all types while a 1911-style half-cock notch allows the TTU to meet or exceed military specifications for drop safety. Pre-assembled, CNC-machined trigger housing contains H13 heat-treated trigger, hammer, sear and a stainless steel spring for trouble-free installation. Wilson Combat AR-15 Tactical Trigger units will reliably function in any standard USGI style AR-style lower receiver with standard GI trigger pins of .154" diameter regardless of caliber, including 7.62/.308 length AR receivers. Note: The TTU is compatible with the S&W MP-10 .308 AR but the rifle's ambidextrous bolt catch must first be removed to install the trigger unit.