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All about recoil....

Discussion in 'GSSF' started by 1234Havasu, Mar 8, 2010.

  1. 1234Havasu

    1234Havasu

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    I would appreciate it if someone could give me a basic education in recoil. I wish to understand how the recoil of a particular pistol would respond to small changes in bullet weight, muzzle velocity, barrel length, recoil spring or grip. A basic understanding of the why would help it to sink in, but the basic what is more important. Also, I was under the impression that muzzle flip was primarily caused by restricting the rearward recoil of the gun at a point below the center of mass. Many of the posts here suggest that certain calibers inherently have greater muzzle flip than others. Have I been delusional my whole life? Finally, again from reading posts, if two different calibers/loads produce the same internal pressure, does that necessarily mean the recoil will be the same?

    To quote Denzel Washington in Philadelphia, "Explain this to me like I'm a 6 year old".
     
  2. AntediluvianFusilier

    AntediluvianFusilier

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  3. 4Baldy

    4Baldy

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  4. English

    English

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    That is asking a lot! I will assume you are as bright a 6 year old as Denzel Washington's character at the time.

    First of all, recoil is entirely related to bullet momentum and not to kinetic energy apart from a small additional effect from the gas jet as the bullet leaves the muzzle. So, a bullet half the weight and twice the speed of another will have almost the same momentum and, other things being equal, the same recoil. That is, mx2V = 2mxV = 2mv for both where x is just a multiplication sign.

    How you feel that recoil is more complicated but what we can call the absolute recoil is the momentum of the pistol, effectively equal to the momentum of the bullet in the reverse direction, that has to be transferred via your hand and arm to you. Unlike energy, which is not conserved in the same form, momentum is conserved and we just have to find where it goes to.

    If we say a small bullet has mass m and it travels at a high speed V, and the heavy pistol, relative to the bullet, has a large mass M and a low velocity v, then mV =Mv. For any given mV and M, we can calculate the initial recoil velocity of the pistol: v = mV/M. This is one of the most significant figures because it is the speed of the slap of the pistol into the hand that does most of the hurting if v gets high enough. I am ignoring silly things like the underside of Glock trigger guards or S&W cylinder latches that can inflict local pain and damage to skin or bone.

    So a heavier pistol with a decent grip, has less felt recoil because its recoil velocity is lower. Different people have different thresholds above which recoil velocity starts to hurt. Why do you need a decent grip and what are its limits? It is easy to imagine that if it was very narrow, the force per unit area would be higher, the grip would dig into the flesh of the hand more and would then tend to crush and bruise the tissue it is compressing. Equally, if the grip is too wide it will overlap the joints of the thumb and trigger finger where it impacts directly on bone with very little cushioning. In general, these are secondary felt recoil effects which are not as much of a problem as high pistol recoil velocity, but it might explain why some people have problems with the G21 or G20, because it is that little bit too wide, and why many people find the G17 family to have comfortable recoil characteristics relative to single stack magazine pistols of the same weight because the wider, but not too wide, grip reduces the force per unit area.

    You are almost completely right about muzzle flip and most people, as far as I can judge their numbers from posts on GT, are wrong. Where you are not quite right is that the rotational inertia of the pistol also reduces the rate of muzzle flip but not its rotational momentum. Most people are wrong on this, I believe, for two reasons. The most important is that they are not comparing like with like and they are confusing rate of muzzle flip with magnitude of muzzle flip. A fast muzzle flip feels worse than a slow one even if the same effort/energy is needed to control it. So, they say that the .45ACP has a gentle push but the .40S&W has a sharp recoil and flip.

    In fact the mV of the two rounds is close to identical so the absolute recoil is the same. The difference is that the G21 is a lot heavier and has a higher rotational inertia than the G22. In short it feels nicer because the pistol is heavier. You can convert a G20 to .40S&W and it is then a direct comparison to a G21. The converted G20 is as soft shooting as the G21 in a frame of virtually identical weight, size and configuration.

    The other faintly possible reason is the long established belief that slow heavy revolver cartridges have a gentler push than fast cartridges with lighter bullets because they spend more time in the barrel and so spread the impact over a longer time. Without doing the calculation I suspect that this is a matter of heavier handguns again. The handgun has not taken up the slack in the grip before the bullet has left the barrel even with a slow cartridge, so the pistol's recoil velocity is the same by the time that it has taken up the slack between hand a d grip.

    When we come to auto pistols we start with the combined mass of the barrel and slide recoiling backwards with some velocity relative to its mass rather than the mass of the whole pistol. This momentum is transferred to the frame and then to the hand in four stages. This is made up from the increasing force of the recoil spring as it is compressed, the impact of the barrel as it unlocks and is brought to a stop by the frame, the impact of the slide at the extent of its movement, and the forward impact of the slide and barrel as they impact the frame at lock up.

    Apart from the relatively small slap as the barrel is brought to a halt, all you feel until the slide hits its stop is the equivalent to what your shooting hand feels when you rack the slide by hand, though faster of course - you are feeling the increasing force of the recoil spring against the frame. Then you feel the major slap of the slide coming to a stop. Then you feel the diminishing rearward force of the recoil spring as it accelerates the slide forward and then the forward impact of lock up.

    All this happens to quickly to feel the individual sensations but someone like Ed McGivern could feel what he described as a double shuffle which disturbed his speed. For this reason he used revolvers for his remarkable shooting exploits, but he could use very lightly loaded .38 Specials and did not need the recoil softening effects of the auto pistol.

    This recoil softening effect is very real. The two impacts are separate but the recoil spring absorbs energy as it is compressed. This reduces the slide speed and so its slap effect is reduced. Instead of getting all the recoil in one slap as you would with a revolver it is spread out in reduced doses. The main impact slap of the slide against its limit (not the slide catch!) is significantly less than would be the case with a revolver of the same weight firing the same cartridge.

    Once the slide has hit its stop and come to rest, the total recoil has been delivered to the frame but you then feel another rearward push as the slide is accelerated forwards, this all feels like the same thing of course, which is almost immediately countered by an equal and opposite push or impact, as the slide returns to battery. I think this push forward and downward flip is what McGivern complained about. It is also why top competitors in high speed gun games prefer low strength recoil springs. They don't reduce the felt recoil but they do reduce the downward sight disturbance at lock up.

    Gun games do not have the same priorities as self defence where a light, easy to carry, pistol has a high priority. A gamer can use a heavier pistol to reduce felt recoil and to steady his aim with advantage and he does not have to carry it for hours a day. For self defence, heavier felt recoil is a price worth paying for a light, easy to carry, pistol. Felt recoil is still the limiting factor to the "power" of pistol you can use and felt recoil is reduced by a heavier recoil spring because it absorbs more energy before the slide reaches its limit.

    Wow! I think that is it apart from minor things I have neglected on purpose.

    Agh! No it isn't. If you think of power as kinetic energy, or K.E., then, if we return to our original recoil example which I represented as mx2V = 2mxV, then the half weight double speed bullet has twice the K.E. of the other because K.E. is directly proportional to mass but proportional to the square of velocity. The square of the double velocity is 4 times that of the lower, but the doubled mass of the slower divides it by two and you get a final double K.E.. You can adjust this ratio up and down the relationship but in general you can have more K.E. for the same absolute recoil by using a lighter faster loading. There are practical limits to this but that is another question or two.

    English
     
  5. HAMMERHEAD

    HAMMERHEAD

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    One thing Wiki left out was the time factor. Modern auto pistols spread the recoil pulse out over time by storing some of it in the recoil spring. A .38 special revolver and a 9mm auto that weigh the same, shoot the same bullet, and at the same speed, the auto will likely have less felt recoil. Total recoil force would be the same, but the peak impulse of the revolver would be sharper and quicker.

    Muzzle flip/rise is a factor of the center line of force (the barrel) being higher than the center of resistance (your hand). The greater the height of the bore above your hand, the greater the muzzle flip in general.
    In a single action revolver this can be a good thing. Shooting heavy recoiling calibers with a high bore axis combined with a grip shape that allows the gun to 'roll up' in your hand reduces the direct impact against the palm of your hand by tuning some of the recoil force into the twisting motion.
    Imagine a .44 magnum where the barrel was in perfect alignment with your hand/forearm. The recoil would come straight back into your bones.

    Recoil is generated by the internal pressures pushing backwards against the case head. Basically it's the pressure times the internal area of the case head.
    More pressure, more recoil.
    Bigger case with the same pressure, more recoil.

    The speed of the pressure, that is how fast the powder burns, and for how long is a factor too.
    Two cartridges with the same peak pressure, but one has a slower burning powder. The slower powder will generate more recoil, and more bullet speed as well (in general).

    It's not actually the bullet that causes recoil, the bullet is actually trying to drag the gun forward. If you had a magic bullet that could drive itself out of the gun, recoil would pull the gun forwards, not back.
     
  6. diamondmike

    diamondmike

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    To put it in a nut shell a heavy bullet has more recoil than a lighter one but caliber plays a major role in recoil of course.

    One thing to remember recoil can cause what is called Limp Wristing in a semi-auto and cause it to jam.
    Limp Wristing is more common in the smaller semi-autos because its harder to get a good grip and the lighter gun will recoil harder.
    One sure sign of Limp Wristing is when you start getting hit in the face and or forehead with casings ejected from the gun.
    This means your wrist got weak from shooting even though you may not feel the weakness.

    After shooting for many years you no longer even notice the recoil even though its still there.
     
  7. fnfalman

    fnfalman Chicks Dig It

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    True recoil is different than felt recoil.

    You put a gun on a frictionless surface or hang it from a string and fire it, you will find that the recoil is simply Newton's 3rd Law of Motion Conservation of Momentum where Mass1 x Velocity1 = Mass2 x Velocity2.

    Felt recoil is a lot more complicated. That's where bore axis, grip angle, auto vs wheelguns, recoil operated autos vs blowback autos, ad infinitum.

    Felt recoil has to deal with the mechanic of how the recoil impulse from the gun transmits to the human body usually via the hands or shoulders.

    Assuming two guns; a wheelgun and an auto, both shoot the same caliber from the same box of ammunition, and both weight exactly the same.

    Hang them on strings or let them sit on an air hockey table and fire the guns, they will go back the same distances at the same velocity.

    Hold them in your hands and it will tell a different story. You will feel the recoil of the auto less than the wheelgun. In the auto, the slide goes backward until it hits the stop then the recoil is fully transmitted to the gun's frame and then to your hand. There's a delay period in your body experiencing the recoil from the gun. With the wheelgun, you shoot and the whole gun pushes against your hand immediately.
     
  8. Girevik61

    Girevik61

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    Meet Recoil...

    [​IMG]

    700 grain .500 Magnum at over 1200 fps.
     
  9. HAMMERHEAD

    HAMMERHEAD

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    Yup, that's recoil alright.
    What kind of revolver do you shoot that in? I bet it doesn't have a scandium frame!
     
  10. Girevik61

    Girevik61

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    Magnum Research BFR, I kind of like them...

    [​IMG]
     
  11. THplanes

    THplanes

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    This is all complete nonsense. You might want to look at this site for the math.

    http://www.loadammo.com/Topics/August01.htm

    The only way presure afects recoil is after the bullet leaves the barrel.
     
  12. 1234Havasu

    1234Havasu

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    A BIG thanks to all who contributed. Now I must read, reread and 3read all this info and digest.

    Larry