MAGAZINE NOT INCLUDED. The Adams Arms AA-15 5.56 is a highly regarded, short-stroke piston-driven AR-15 rifle known for offering a cleaner, cooler-running alternative to traditional direct impingement (DI) rifles at an accessible price point. Unlike standard AR-15s that vent gas directly back into the bolt carrier group, the AA-15 vents carbon and gas forward at the gas block, making it exceptionally reliable and popular for suppressed shooting.