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!

31 thoughts on “Why do some airguns recoil? – Part 1 Spring-piston guns

  1. Hi, sorry if this is posted in the wrong place- I have not yet got to grips with Blogging if thats what it,s called ! Just wondering if you know of a relationship between optimum barrel length for a springer and swept volume of the compression cylinder in trying to extract maximum velocity from a given powerplant ? you catch my drift ?

    Wazza


  2. Wazza,

    A spring gun barrel doesn’t need to be long at all. About 9-10 inches is the maximum length needed for max velocity. After that, it’s all for show.

    Springer use so little air that they do not benefit from long barrels the way pneumatics and CO2 guns do.

    B.B.



  3. i know youll probly get to this tomorow but when i pump my 392 all 8 times i do notice slight recoil. i think this is because the air pressure pusses backward on the bolt as much as it pushes on the pellet.




  4. golgo

    i have a question for you B.B.If a pellet does not fly like a bullet which i stabalized from the rifling of a barrel and a pellets is stabalizes by the skirt produced by the piched waist.Then why do some guns shoot the same pellet more accuratly than other if accuracy is dependent of the quality of the pellet.And considdering that an rifled air gun does not spin the pellet enough to stablize it in filght how can this be? Shouldn’t all guns shoot the same pellet the same way then.Im just taking a wild guess here but if 90% of in flight stability is from the pellet and not the rifling then how is that possible that one make/model of a gun can far out preform another make/model shooting the same exact pellet if a gun can only diliver 10% accuracy but yet out shoot its competiter by 20 to 30 or even 50%??????”WTF”? am i missing something here or am i just stupid


  5. bb,
    How do you rate the M14 airsoft sniper rifle on Pyramidair. Is it a good gun or should i look at a different airsoft sniper rifle? I own 2 ICS full auto rifles that are really good that ive had for two years and i use alot but i want a good sniper rifle to add to my collection without spending a mint


  6. P.S. Thanks for the advice on using transparent BB’s for airsoft sniping to help conceal your position. I never would of thought of that.


  7. Hi there,

    Vince posted a link the other day to this site showing the teardown of the IZH61:

    http://www.eaacorp.com/diagrams-izh61lg.html

    All parts are shown EXCEPT the screw just towards the front of the top surface of the receiver just back from where the number 44 shows in the diagram. That is a screw that seals the lube point for the transfer port. Its made of the same material as the receiver, and after I took mine out to put in some oil (pellgunoil) it doesn’t want to do up tight. I put it back in gently, ensured the thread wasn’t crossed by backing it up a bit, and screwed it down with as little torque as seemed necessary, but it goes in and then will just rotate as if the thread is gone. Before I took it out it was sealed from the factory with some gunk that had set. The same gunk was on the threads of the barrel where it screws in to the receiver. Anyone had any epxerience with this?

    Gazza.


  8. Hello: Kind-of on topic. For those that want a smoother, quiter and much less problems with hold and recoil in there Gamo 440, a easy TUNE-DOWN does wonders. Mine is at 800 fps with 8.3 gr pellet. Real Nice. My Shadowmatic is now at 750 fps, a better speed for the match pellets it needs for it’s tube magazine. Solves a pile of problems associated with these rifles.


  9. golgo,

    You have raised an interesting question. I believe that some air rifles are so poorly bored that they HURT the stability of the pellet! Chinese rifles are a good example of this. Many of the older cheaper models are so overbore that they can be outshot by a smoothbore airgun.

    There are other factors that contribute to accuracy besides the rifling. A bore can be choked and contribute a huge amount to the accuracy.

    Also, the hashness of the powerplant can deform pellets with thin skirts. That hurts accuracy as well. This is true for spring pistons guns, which is where the most inconsisteant accuracy come from.

    Finally the spring piston gun is a challenge to shoot accurately. Many of them do not shoot as well as they could because the right technique is not used. Other springers like the TX200 are more forgiving and more of their true accuracy comes through regardless of the hold.

    B.B.


  10. M14,

    Okay, I found it. I was surprised by the term SNIPER applied to the M14. That is not its primary role.

    Then I looked at the gun. Interesting, but hardly a sniper rifle. Where is the scope rail?

    This model is quite interesting for the power it offers, but without a scope, how can it be used for sniping? I don’t know, but if you are interested, this one sounds like it’s worth a look.

    B.B.




  11. Gazza,

    While I’m not familiar with this, it does sound like some threads might’ve gotten stripped. If it’s just a screw, can you buy one (hardware store) and trim it down as necessary?

    BTW – I believe that BB has made the point that Pellgun oil is NOT for springers. It’s for pneumatics and CO2 guns.


  12. golgo

    BB what do you mean by choke and how does choking a bore contribute to a larg amout of accuracy?can you also give some examples of choked bore guns for contrast with other none choked guns.
    thanx’s


  13. 392 recoil,

    I suppose you can look at it as the air pushing against the bolt, but that leaves out its relation to the pellet. Technically it is a reaction to the air (or CO2) and pellet being pushed out the barrel. “For every action there is an opposite and equal reaction” as we learned in Physics class. Therefore the gun must move backward with an energy equal to the air and pellet going forward.



  14. Greetings bb,

    Will not the recoil of any gun be governed simply by conservation of momentum?

    Sure, a springer may lurch forth and back as the spring relaxes, causing an impulse to be delivered to the shooter which very well may disturb his aim. This impulse will also transmit some small amount of energy to the shooter’s mass, however at the end of the day (or the end of the shot in this case) the net recoil of the gun system must equal the released momentum of the ejecta.

    I believe firearms are traditionally discussed in terms of free recoil, which includes the mass of the gun, but ignores mass of the shooter.

    Momentum of ejecta = Momentum of gun in (free) recoil

    Ejecta would include the projectile as well as the propellant mass released.


  15. BB…Gamo 440 type Tune…Started with clean-up and a relube with J.Maccari moly on the piston and his tar on the spring. Shortened the spring (one end only) and the plastic rear spacer,(abt a 1/8″ from each end) they use for what looks like a spring pre-load device for this series of guns. The cut end of the spring goes into the piston side. (finish-up spring tip) It now has ABOUT a 2 inch spring pre-load. To remove the spring l let it shoot into a leg of some old blue jeans. to reinstall the spring I use a woodworkers 36″ bar clamp and a simple fixture. I’m sure there are many reasons for doing the above a better way, but this works for me.


  16. Momentum,

    In an airgun, the timeing of the release of energy can be absorbed by the gun so it doesn’t transmit as a sudden impulse. Yes it’s there, but you don’t notice it. It’s like the difference in felt recoil between a Springfield 1903 and a Garand. Both fire the same cartridge and have the same momentum, but the Garand feels much lighter, because it lasts much longer.

    B.B.



  17. The recoil energy of a spring gun WON’T equal the energy of the air and pellet expelled. When you cock a spring gun you use energy (muscle work) to store potential energy in the spring. When that energy is released as kinetic energy, only part of it is transferred to the air and pellet. The rest will end up as heat and recoil (there is also recoil that is the reaction to the pellet and air action).

    If all the energy transferred to the air and pellet, the piston would come to the end of its stroke and not vibrate, move the gun, or anything. It would just stop. Then you would ONLY have the recoil that is a reaction from the air and pellet. Of course this situation is impossible.


  18. Impossible:

    I believe you confuse energy and momentum.

    Yes, you store energy in the spring. This is no different than the chemical energy stored in gunpowder, or the energy stored in rocket fuel.

    Conservation of momentum still applies.


  19. Momentum:

    You are correct that I didn’t address the momentum issue. The momentum of the air, oil, pellet, etc. (ejecta) won’t equal the momentum of the gun because of the extra force which the spring applies to the gun. This force changes its momentum. Yes, the momentum of the whole system will be conserved, but the variables are not just the ejecta and the gun.




  20. Impossible:

    I’ve been pondering this all day and I must still (politely!) disagree.

    The force which the spring exerts upon the airgun is no different than the force which expanding gaseous gunpowder exerts upon the firearm. Conservation of momentum is conservation of momentum. Physics allows no exceptions.

    It is also true that the stored energy is partly allocated to the projectile, but much is wasted into heat in both types of gun.

    However, what I’ve been missing is the fact that when the spring relaxes, its center of mass changes, which amounts to motion that must be accounted for. So yes, your intuition that momentum of ejecta DOES NOT exactly equal momentum of gun has merit.

    Consider the Whiscombe rifle bb has so kindly described for us. His description implies that it has symmetrical springs, the center of mass of each changes when released, but at the system level they cancel. There is no change in “balance” of the gun mass. No change in mass center means no momentum to generate recoil. In this case the momentum of ejecta DOES equal momentum of gun.

    I believe this description is more accurate, but I’m open to inputs from others who may have better understanding.


  21. i have a rws 350 magnum.and every 30-45 shot in heat outside will heaten the spring.what do i do to fight that heat.please help with simple terms.


  22. There is no way an airgun mainspring can heat up while shooting. Even in the desert in 120 degrees, the spring could not heat up.

    Why do you think your spring is heating? What symptom does the gun display?

    B.B.


Leave a Reply

Your email address will not be published.


6 + 7 =

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>