25 psi was all it took to accelerate a 4-lb. projectile to 190 fps

Thursday, January 27th, 2022

At SHOT 2022′s Industry Day at the Range, Umarex unveiled their brand new Primal 20, an airgun designed to shoot 20-gauge slugs:

Air guns can operate with surprisingly low pressures:

I have been saying this for a long time — barrel length is an important part of precharged efficiency — maybe the most important part! On the Mythbusters TV show, they shot a 4-lb. chicken carcass from an air cannon at 130 m.p.h. on just 25 psi! When they bumped the pressure up over 100 psi, four times as much, the velocity increased by less than 5 m.p.h. So, 25 psi was all it took to accelerate a 4-lb. projectile to 190.7 f.p.s. when shot from an 8′ cannon barrel.

Airguns from history got high velocity from very low pressures. Typically, they were pressurized to 500 psi, yet had the power to launch a .50 caliber lead ball with enough force to kill deer-sized game beyond 100 yards. The recorded velocities of the vintage big bores are in the 500 to 600 f.p.s. range. It wasn’t just long barrels that produced such remarkable results — they also had air valves that remained open far longer than modern PCP valves do.

In Airgun Revue No. 5, Tom Gaylord wrote about a Gary Barnes’ big bore rifle that shot a .457 caliber lead ball at 800 f.p.s. on just 750 psi! That rifle had 10 good shots at that pressure! The barrel was over 32″ long, which is long but necessary for low pressure to accelerate a projectile to high velocity.

If you’re not familiar with Lewis and Clark and their air rifle, it’s a fascinating bit of weapons technology.


  1. Dave says:

    The velocity of a .45 ACP round, used in the 1911 Army, is about 830 feet per second. With hollow point bullets, it is very lethal. Double the pressure in the air rifle to 1500 psi and the same velocity can be obtained in a 16-inch barrel, the same barrel length as the standard M4 carbine. A standard scuba tank has a pressure of 3000 psi, providing a large air supply through a flexible hose. Replace the cone in a fully-automatic paintball gun used to hold the ammo with two flat plates separated by the length of the hollow point, and you would have a relatively quiet 45 caliber machine gun capable of firing far more rounds without reloading than a WWII M3 machine gun. Who needs a 3D printer for mayhem?

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