Why do some airguns recoil? – Part 1 Spring-piston guns
by B.B. Pelletier
Actually, ALL airguns recoil. Even the match guns that use compressed air recoil. Otherwise, why would Steyr and Feinwerkbau add hundreds of dollars of technology to their guns to cancel it?
Today, we’re going to talk about why airguns recoil. I’m not an engineer, so my explanation will not be very detailed, but I hope to shed some light on the way recoil works in all three powerplants. And let’s start with the most obvious one.
It doesn’t matter what type of spring is in your gun
This discussion includes all spring types, coiled steel, gas and elastic band. Though the springs may differ, the powerplants all work the same. Refer to the drawing that illustrates the explanation.
Regardless of the type of spring, all spring-piston powerplants work alike.
Cocking makes the piston either stretch or compress the spring
Compression is most common, but a few guns have used a stretched mainspring. The piston is held in place by a latch, called the sear. When the trigger releases the sear, it releases the piston, which is then free to move. The spring, which is under tension from compression or stretching, is now free to return to its relaxed state. It moves the piston as it goes. This action produces some recoil.
The weight of the piston’s movement acts on the rest of the gun, however the gun is so much heavier that it moves very little. Let’s use air rifles for this discussion to bound the specifications a little. Pistons weigh between 7 and 16 oz., while the guns they are in weigh between 80 and 160 oz. The amount of recoil transmitted to the gun is small in proportion to its weight. If the piston moves forward, then the gun moves backward. This first recoil is very light and may not be noticeable to the shooter.
When the piston stops, it can produce significant recoil
At the end of its travel, the piston comes to a sudden stop. The force of that weight, driven by a strong spring, has built up momentum to the point that a sudden stop sends a jolt of energy to the rifle. Instead of moving in the opposite direction, this time the rifle moves in the same direction the piston was traveling. If that was forward, as it most often is, the rifle jumps forward. The amount of the jump (forward recoil) depends on the weight of the piston, the weight of the rifle, the strength of the mainspring and the time it took the piston to slow down at the end of its travel. The longer the deceleration, the less energy transmitted to the rifle.
The second recoil is the most noticeable. Because it is forward more often than not, it jolts the rifle forward. Webley Patriots have a lot of it, as did FWB 124 rifles. A rifle with a long piston stroke tends to have the most forward recoil, unless something has been done to dissipate it. This is also the jolt that is so hard on scopes.
But aren’t some spring guns recoilless?
Yes. And no. Some guns, such as the Whiscombe and certain Diana target guns, cancel the recoil. There are others that recoil but isolate the shooter so he doesn’t feel it, such as the RWS Diana 54. For every action, there is a reaction…and recoil is its name.
Next time, I’ll address both CO2 and pneumatic guns. They operate on compressed gas and react the same to firing. And, both recoil!
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