The Presma 3.5-inch short buffer tube kit is the shortest pistol-length receiver extension we stock for AR-15 pistol builds running 5.56 NATO or 300 BLK. Drop-in fit on any standard AR-15 lower receiver - no proprietary parts, no gunsmithing, no permanent modifications. At 3.5 inches, this short buffer tube produces a compact overall length while still cycling a standard carbine recoil spring and a single-piece BCG insert in place of a conventional buffer. The result is a noticeably shorter pistol that handles cleaner on the brace and stays out of your sightline when shouldered. It is a popular choice for ultra-compact 7.5" and 8.5" pistol builds, PDW-style platforms, and shooters running an SB Tactical or Maxim Defense brace where every inch of overall length matters at the bench or in a backpack. Kit contents: 3.5" pistol buffer tube Buffer tube end cap Receiver end plate Castle nut Guide rod Carbine recoil spring Bolt carrier insert Wave spring Compatibility: 5.56 NATO and 300 BLK AR-15 pistol uppers. Not compatible with 9mm AR pistol uppers - the geometry is built around rifle-bolt cycling, not blowback. Function-check by hand-cycling the BCG after assembly - if the bolt rides smoothly into battery under spring pressure, the kit is seated correctly. Apply medium-strength thread locker to the castle nut and torque the receiver end plate flat against the lower before staking.