The Adams Arms Piston Drive System uses the same gas port on the barrel to work the action of an inverted piston. Instead of directing the gases into the receiver, they go into a gas plug and drive rod sleeve invented by Adams Arms. The gases are contained inside the drive rod sleeve and push the bolt carrier rearward using the gas pressure to cycle the action. Adams Arms proprietary operating systems mechanically actuate the bolt carrier external of the receiver. This keeps the internal receiver and all the critical moving parts clean and free from heat and carbon build up. The Piston Rifle Length model is a short stroke free floating piston system. It is self-cleaning, has a corrosive resistant coating, and eliminates flash signature and super sonic crack which is optimal for night vision and suppresses fire. The kit includes: patented one-piece bolt carrier; adjustable P Series micro block; upper receiver bushing; bushing installation rod; bolt spring; drive rod with bushing and spring.