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Physics behind "Push" vs "Snap"

Discussion in 'General Gun Discussions' started by RTR_RTR, Mar 17, 2011.

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  1. RTR_RTR

    RTR_RTR Member

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    Hey guys,

    Push (.45) vs snap (.40) recoil came up in a thread a while back, and I couldn't figure why this might be. Anyone have any solid knowledge or or want to just hypothesize for that matter? The three most logical things I can think of are barrel height relative to hand (higher, more snap), gun weight (higher, more push), and powder burn rate (higher, more snap). The gun-related factors would obviously be contingent on, well, the gun used, but there may be trends in design between the guns firing the respective caliburs (e.g. all metal 1911 .45, polymer frame glock .40).
     
  2. WardenWolf

    WardenWolf member

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    Mainly it's the projectile's velocity to weight ratio. Higher-velocity rounds will tend to snap more, whereas the .45 is a big, slow round, and gives more of a push. In long guns, the analogy would be that a shotgun is a push, whereas a rifle is a kick.
     
  3. General Geoff

    General Geoff Member

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    Recoil impulse is dependant on many factors, the most important ones being mass of the gun, mass of the projectile, and velocity of the projectile.


    Those three figures can be used to figure the missing fourth: velocity of the gun coming back towards you. Simple laws of physics, every action has an equal and opposite reaction. Different bullet weight and velocity will result in different gun velocity (i.e. recoil).
     
  4. Cryogaijin

    Cryogaijin Member

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    Velocity. The recoil is spread out over the duration of the firing of the gun. Slower the round, "slower the recoil"
     
  5. SleazyRider

    SleazyRider Member

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    What an interesting question! Here's my read:

    We humans are used to thinking in terms of our own human time frame, and not necessarily that of the physical world. So what we define as a "snap," in our terms, is really an eternity compared to, say, the speed of light. Same with an automotive engine spinning at 10,000 rpm; though it's hard for us to conceive of it in this way, the four-stroke cycle is really occurring as slowly as molasses.

    So I opine that the "snap" vs. "push" is really a function of the speed at which the powder flame propagates, or changes from a powder to a gas, assuming all other things are relatively equal. I think reloaders call it deflagration or something similar.

    Please feel free to shoot me down on this, as it is only my notion, and I don't mind being corrected.
     
  6. RTR_RTR

    RTR_RTR Member

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    Sleazy, that's actually one of the things I'm leaning toward, if I wasn't clear in my op.

    I'm not sure I buy the velocity argument. Velocity alone doesn't have any direct relationship that I can see in HOW a gun will kick - just to what degree, and that's only assuming increases in velocity over an equivalent time span (i.e. impulse).

    My rationale behind the quicker burning powder is less time to react to the kick, thus having the brunt of the force taken in the wrists, which don't have enough reaction time to respond properly by locking up.
     
  7. SleazyRider

    SleazyRider Member

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    This suggests another question as well: Since there's always a muzzle rise upon ignition that tends to push the muzzle off target, is it logical to assume that the sooner the bullet leaves the influence of the moving barrel the better? In other words, all other factors being equal, is a faster-burning powder inherently more accurate?
    On second thought, assuming the mass of the bullet remains constant, a greater force is required to increase its acceleration. Does a faster burning powder create a greater force?
    Dang, that's more thinkin' and speculatin' than I'm accustomed to doing this early in the morning!
     
  8. fletcher

    fletcher Member

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    I'm going to hypothesize that the rate of change of momentum imparted to the shooter is the main factor for felt push/snap. Faster = snap, slower = push.

    EDIT: Clarifying that the above is all related to, and can be defined with, force, mass, acceleration, etc.
     
    Last edited: Mar 17, 2011
  9. btg3

    btg3 Member

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    Acceleration is velocity change over time -- ie, the derivative of velocity.
    Force = Mass * Acceleration
    Momentum = Mass * Velocity

    Faster burning powder creates greater force to the extent that in generates higher acceleration of the bullet. What else might affect acceleration? Amount of powder, volume change upon combustion, caliber, barrel length, how much gas escapes via other routes than the barrel tip...

    Does push/snap begin only after the bullet exits the barrel or before? If before, is POA/POI affected? If not, are we discussing perceived push/snap as opposed to a true difference?
     
  10. geekWithA.45

    geekWithA.45 Moderator Emeritus

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    It's a function of the curve of how the total amount of force is applied over time.

    Assuming for the sake of argument the same total force, we can visualize how our 25 hypothetical units of force are distributed over time in a graph, which due to the limits of its character nature is arranged so that force increases to the right, and time increases going downwards.



    "Snap":

    ----------force----------->
    |*
    |*
    T***
    I****************
    M***
    E*
    |
    V

    "Push":
    ------Force-------->
    |*
    T*
    I**
    M***
    E****
    |*****
    |******
    |***
    V
     
  11. fletcher

    fletcher Member

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    ^ That's a good visual representation for what's going on. The longer it takes the bullet to leave the barrel (slower acceleration), the longer a force will be applied, and the "pushier" it will feel.
     
  12. grizz13

    grizz13 Member

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    Not sure how great of an effect this would have but with the 40 being a higher pressure round could the forces of the compressed gasses leaving the muzzle after the bullet has left be the main factor. The 40 would decompress much faster than a 45 due to the greater pressures generated. Just a guess. So the big question is who has the equipment to start doing some tests?
     
  13. ball3006

    ball3006 Member

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    I guess I am showing my age. I always thought it was called recoil.........chris3
     
  14. DoubleTapDrew

    DoubleTapDrew Member

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    My thinking is along the lines of grizz.
    Pressure
    .40 S&W: 33,000psi
    .45 ACP: 21,000psi
     
  15. Walkalong

    Walkalong Moderator

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    Yep.

    It is the velocity reached and the quickness with which it gets there that gives a push or a snap.
     
  16. KodiakBeer

    KodiakBeer member

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    Well, it wouldn't be velocity alone. A .45 can be loaded to .40 velocities with 165 grain or 185 grain slugs, but it still doesn't "snap".
     
  17. General Geoff

    General Geoff Member

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    I submit that given a similar platform of the same weight (say, Glock vs Glock), a .45 loaded to .40 caliber specs in terms of bullet weight and muzzle velocity would have perceptibly identical recoil.
     
  18. LKB3rd

    LKB3rd Member

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    I am gonna go for the KISS answer:
    People need different words to describe slower or faster recoil. Push=slower, snap=faster.
     
  19. KodiakBeer

    KodiakBeer member

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    Could be. Anybody got a matching set of .40 and .45 pistols?
     
  20. Maverick223

    Maverick223 Member

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    I agree (though actual recoil would be imperceptibly greater due to the lower pressure .45ACP requiring a bit more powder). In short, weight and the use of a heavier projectile (thus lower velocity) are the primary differences.

    :)
     
  21. brickeyee

    brickeyee Member

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    The rate of change in acceleration is called 'jerk.'

    It occasionally comes into play, but is often so variable that it cannot be easily managed analytically.

    Higher jerk indicates more of an impact than a push.
     
  22. NMGonzo

    NMGonzo Member

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    Given the same weapon and bullet mass, the higher the muzzle velocity will be snappier.

    .44 special vs .44 magnum for example, same weight bullets and all, the .44 magnum will feel snappier TO ME.
     
  23. Nushif

    Nushif Member

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    I'd agree with this and venture to say that slide velocity is probably a huge factor here, as it's the part that actually imparts the kinetic energy into our hand.
     
  24. awgrizzly

    awgrizzly Member

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    I would venture a guess that it's a shooter's imagination, probably due to the sound... one goes boom and the other goes bang. =o)
     
  25. Walkalong

    Walkalong Moderator

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