Ar9 pistol. This is your ultimate guide for 2020/21 and beyond! We’re breaking down everything you need to know to build one yourself: What the AR9 pistol is, what separates it from an AR-15, parts compatibility, 9mm Parabellum’s ballistics, buffer weight, barrel length, twist rate, and magazines. When we’re through, you’ll know everything you need to build the perfect AR9 pistol in a supersonic or subsonic (suppressor-friendly) configuration. Looking for answers about shouldering an AR pistol brace?. All data and recommendations in this guide were compiled from real shooters who’ve built and tested AR9s with different parts.
What is an AR9 pistol?.
Ar9 Pistol. (sometimes hyphenated “AR–9″) is a new 9mm variant of the AR-15. But this particular 9mm weapon is not just an AR–15 with a 9mm Parabellum conversion kit installed. Converted 5.56/.223 guns use special parts to adapt the factory upper and lower receivers for the 9mm cartridge. The AR9 pistol instead uses a new lower receiver aptly called the (Ar9 lower) and a stripped AR–15 upper receiver with a 9mm barrel, new bolt carrier group, and an AR–15 buffer system and lower parts kit. A 9mm–specific buffer is required inside your buffer tube, but we’ll touch on that later. Since the AR9 pistol and AR–15 appear so similar, let’s compare the two first.
How the AR9 Pistol is different from the AR-15.
Ar9 Pistol. The AR9 and AR–15 look alike, but each uses different parts and systems to operate. There’s a lot of discussion – and some confusion – about how these two guns work.
The AR-15 Pistol uses gas or a piston.
The AR–15 uses a direct–impingement system with a gas tube to cycle the bolt:
- The firing pin hits the primer on the rifle cartridge.
- Powder burns in the chamber, accelerating the round.
- Excess gas travels to a gas port and through a tube or piston.
- The gas/piston travels back into the upper receiver and bolt carrier group.
- A key atop the bolt traps the gas/piston and allows it to drive the bolt into the buffer.
- The spent casing is ejected, the bolt drives forward, and a new round is chambered.
Why the AR9 Pistol can’t use a gas tube.
A rifle round has a lot of powder. It produces a lot of gas when fired, and burning all that powder takes time. This is the only way to achieve the right amount of velocity a rifle round requires. But all that round’s energy would 1.) quickly destroy the bolt and trigger group, or 2.) not cycle the bolt completely in a blowback-operated AR-15. That gas must expend more of its energy on the bullet itself before being harnessed to cycle the bolt. This is called dwell time, and it’s why gas must travel down the barrel and through a gas tube before coming back into the receiver. This is also why AR–15s have different gas system lengths. Some rounds and barrel lengths produce less pressure. Some produce more pressure and require more dwell time to avoid over-pressurizing the receiver.