This system will work with 300BLK and a Pistol Length Gas System. - Kit includes: - Patented One-Piece Low Mass Bolt Carries - P Series Micro Block - Adjustable (5 Settings - 100%/74%/53%/32%/11%) - Bolt Spring - Drive Rod with Bushing and Lightened Spring - Installation Instruction Card - Our Piston Kits No Longer Require the Receiver Bushing or Installation Dowel - The Adams Arms Piston System: - A short stroke free floating piston system. - Is Self-Cleaning. - Carbon and gases are expelled forward away from operator. - Corrosive resistant coating processes. - Harmonics are not transferred into the barrel. - Doesn't vent directly to atmospheric pressure; this eliminates flash signature and super sonic crack which is optimal for night vision and suppresses fire. - Has a Lifetime Warranty. - For 300BLK we only recommend a Pistol Gas Length (4.846 from barrel extension to shoulder) and a Low Mass Carrier for optimal performance. - We recommend using a standard barrel nut or barrel nut with similar measurements for proper fit and function of the kit. Many aftermarket proprietary barrel nuts do not offer the clearance for the drive rod or proper seating of the spring and bushing. - Micro Gas Blocks should have the set screws torqued to 55-60 in-lbs