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Airgun Guru: Recoil

PUBLISHED: 10:32 12 April 2016 | UPDATED: 10:32 12 April 2016

Some manufacturers use slightly heavier piston weights to get the .177 up to power, which will slightly increase the recoil

Some manufacturers use slightly heavier piston weights to get the .177 up to power, which will slightly increase the recoil

Archant

Q: I’ve read recently that with identical guns, the .177 recoils more than the .22 version. It’s not a subject I’ve given much thought to, but I recently bought an early ‘90s HW35 .22, putting out a little over 11 ft. lbs. I also have a nearly new HW35 .177 which does 11.4 ft. lbs. The latter has far harsher recoil. Why is this? Bru

GURU SAYS: The .22 is intrinsically more efficient at converting energy stored in the compressed air into pellet energy than the .177, and that applies regardless of whether the airgun is a springer or a PCP.

I don’t pretend to understand all the physics of the airgun, but in a nutshell, because the .22 pellet takes longer to travel up the barrel than the faster .177 pellet, the air pressure is acting on it, and accelerating it, for longer, and so more energy is transferred from the air to the .22 pellet.

In order to get the .177 to produce the same muzzle energy as an identical .22, the piston needs more force from the spring to push it a fraction further toward the front of the cylinder and generate higher cylinder pressure, and that will result in a small (a very small) increase in recoil. With your .177 producing 0.4 ft. lbs. more than your .22, the piston will need yet more spring force, and produce yet more recoil, but - and it’s a very big ‘but’ - the difference in recoil travel will be so slight that I doubt you’d be able to feel it.

I think your perception of greater recoil from your .177 is quite possibly more caused by increased piston (and hence recoil) acceleration than the longer compression stroke. Our perception of recoil is also greatly affected by what happens inside the springer after the piston has reached the end of the compression stroke. In extracting more energy from the air, the more efficient .22 is leaving less energy in the air that becomes available to push the piston back up the cylinder, which causes the second, forward part of the recoil cycle.

With less energy to drive piston bounce, the piston does not bounce as far back, and compresses the mainspring less, so that the second forward piston stroke, long after the pellet has left the muzzle, is shorter, slower, and gives the piston a softer landing. The less efficient .177 will have greater piston bounce, will compress the spring more, and will give the piston a rather harder landing, and I believe that this also contributes to our perception of recoil.

GURU TIP: In cold damp weather scope lenses can fog up obscuring your sight picture. Carry a small lens cloth in a plastic bag to clear them rather than risk scratching the coatings

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