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Gun Question - Recoil. Before or after bullet is clear?

Discussion in 'General Gun Discussions' started by Sean Dempsey, Nov 17, 2008.

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  1. Sean Dempsey

    Sean Dempsey Member

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    I have a general, non political gun question!


    It's simple - has the bullet cleared the end of the barrel before there is significant recoil movement? For instance, if we had a super super slow motion camera, could we view the bullet leaving the barrel before the gun appears to recoil back at all?

    Also, has the bullet left the barrel before say, the slide on a handgun moves, or the bolt in a rifle moves?

    Just curiosities, thanks!
     
  2. jnyork

    jnyork Member

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    Recoil begins the instant the bullet starts moving. The "opposite and equal reaction" thing. You can easily observe this by firing a handgun with two different loads, one very light and the other one full power. The light load will shoot quite a bit higher due to the bullet being in the barrel longer while the barrel is moving up with the recoil.
     
  3. Sean Dempsey

    Sean Dempsey Member

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    Yeah I realize newtons law is in effect, but I was curious as to say, what is the distance the barrel climbs in the time it takes for the bullet to clear the end of the barrel. A few nanometers?

    Some really, really dirty math and I figured that a bullet from a 9mm could clear a 3" barrel in .0003 seconds, or 3 ten-thousandths of a second. So, if that math is even close (which it probably isn't), I wonder how far the recoil of a barrel is in the same .0003 seconds?
     
  4. everallm

    everallm Member

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    Actual or felt recoil?

    In simple Newtonian physics, for every action there is an equal and opposite reaction. However.......

    The recoil impulse is generated at the instantaneous moment of the round ignition and will last as long as the charge is burning. Once the charge has fully combusted, no more energy is being released, no more energy for recoil

    Due to mass and inertia, the rifle will take a finite time to start to recoil and will build over time so the perceived recoil effect will still be occurring after the round has left the barrel.

    If the rifle is semi-automatic and some of the pressurized, combusted gas is tapped and diverted to the reloading mechanism, there is a secondary impulse that can extend the length of time of the recoil.

    The same inertia and lag affects the time it takes a slide, piston or bolt carrier to start and complete a cycle.
     
  5. MAKster

    MAKster Member

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    The simple answer that I think you are looking for is that the bullet is moving so fast that the shooter doesn't feel the recoil until after the bullet has left the barrel. Flinching in anticipation of the recoil will throw off your aim, not the recoil itself.
     
  6. misANTHrope

    misANTHrope Member

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    This seems like something that will not be consistent across the board. I'd expect a large amount of variance between different types of guns, action types, loads, weights....

    The consensus with handguns is that the muzzle does begin to rise significantly before the bullet exits. As noted previously here, this is why lower-velocity loads actually shoot higher.
     
  7. RKBABob

    RKBABob Member

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    Its about time someone came up with one of those!

    Yes, recoil and muzzle rise start the instant the bullet starts to move... as the bullet is propelled forward, the firearm is propelled rearward (and a little upward) in proportion to its weight relative to the bullet. I'd love to see a video of this as well.
     
  8. General Geoff

    General Geoff Member

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  9. Dr. Tad Hussein Winslow

    Dr. Tad Hussein Winslow member

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    The overwhelming majority of recoil happens AFTER the bullet has left the muzzle - BUT, there is *some* recoil movement which occurs while the bullet is in the barrel.
     
  10. BigG

    BigG Member

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    Yep - the bullet cannot move unless the gun moves too. The masses are so different it seems like the bullet leaves before the gun moves, but - nope! The same amount of energy that moves the bullet causes the gun to recoil. It's as simple as that.
     
  11. Sean Dempsey

    Sean Dempsey Member

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    Very interesting that lower velocity rounds shoot higher on target. I didn't know that.

    The ultra-high speed mechanics of gun functions are fascinating to me. The video of the bullet leaving the barrel is awesome, I can clearly see the muzzle start to rise, even if it was only a fraction of a millimeter.
     
  12. benEzra

    benEzra Moderator Emeritus

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    The gun is already recoiling near its full recoil velocity by the time the bullet exits the barrel. However, it has not had time to actually move very far.
     
  13. CypherNinja

    CypherNinja Member

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    *clears throat*

    Muzzle-loader, Single-shot, Bolt-action, Break-action, Lever, "Normal" Revolver:
    1. Ignition
    2. The bullet begins to move due to climbing pressure. Recoil begins in the same instant due to "Equal/Opposite Reactions".
    3. As the bullet accelerates down the barrel, equal force is applied to both the bullet and the breach face (through the case, when present) by the gas pressure. If the gun was suspended from both ends by strings and was free swinging, the momentums of the bullet+gasses and the gun would MATCH during this process. (Revolvers only: When the bullet passes the cylinder gap a very small, but theoretically there, force is applied to the front face of the cylinder by the gasses escaping through the gap.)
    4. When the bullet reaches the end of the muzzle, virtually all of the recoil has already been generated. After the bullet clears the muzzle, a (generally smaller, usually MUCH smaller) force is applied to the muzzle crown and breach face by the residual gasses still escaping the barrel.
    5. Any "recoil" perceived after this point is simply the shooter in the act of slowing the rearward velocity of the firearm and returning it to the ready position.

    All Blowbacks function similar to above. However, all recoil (except the residual mentioned in #4) is first transferred to the bolt (excepting some small rearward force applied through friction to the chamber by the case, and some small forward force applied through friction to the barrel by the bullet, the relative size of these forces could be argued forever). As the bolt travels to the rear, a growing amount of force is applied to the receiver by the recoil spring, as well as some force being applied to the receiver through cocking the hammer, if present. When the bolt reaches the rearward stop, all remaining momentum is transferred to the receiver. Further force is also applied to the receiver as the recoil spring accelerates the bolt forward, and is canceled when the bolt reaches the forward stop. (this is the source of the "lower reciprocating mass is better" arguments)

    All Recoil-operated guns also function similar to above. However, all recoil (including #4) is first transferred to the barrel and slide/bolt (or the "upper frame and cylinder" in automatic revolvers ;)). As the barrel and slide/bolt travel to the rear a growing amount of force is applied to the receiver by the recoil spring, as well as some force being applied to the receiver through cocking the hammer, if present. Additionally, when the barrel reaches it's rearward stop, the barrel's momentum is transferred to the receiver. When the slide/bolt reaches the rearward stop, all remaining momentum is transferred to the receiver. Further force is also applied to the receiver as the recoil spring....etc.....etc

    All Gas-operated guns function the same as above. However, the "reciprocating mass issue" mentioned at the end of the Blowback and Recoil-operated paragraphs is preceded by a force accelerating the gun forward and the bolt carrier rearward after the bullet passes the gas port. Some of this force is canceled out during the bolt unlocking process as well as some force being applied to the receiver through cocking the hammer, if present. All the remaining momentum is canceled when the bolt carrier hits the rearward stop. Further force is also applied to the receiver as the recoil ....etc.....etc


    THERE! DONE! I didn't mention torque/counter-torques, chain-guns, balanced-actions, recoil boosters, bolt accelerators, elastic vs. inelastic collisions, or a few other things, but it seems relatively complete. :scrutiny:

    Pardon any errors, I still need to get some caffeine in me. ;)


    (i r good at teh mechanics, can i has cookie now?)


    EDIT: To clarify, all/most of the various accelerations happen while the bullet is in the barrel. Most, but not all, of the movement happens after the bullet has left the barrel. You can spot all the little movements I mentioned in the video General Geoff linked.
     
    Last edited: Nov 17, 2008
  14. Claude Clay

    Claude Clay Member

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    p239 with its 40 S&W bbl shoots POA
    with a 9mm conv bbl at 25 feet is 2+ inches lower than the 40 group
    with 357SIG conv bbl shoots 2+ inches lower than the 9mm group.
    same gun and shooter; slower is higher.
     
  15. rcmodel

    rcmodel Member in memoriam

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    Just look at the sights on any big-bore revolver.
    The front sight is always much higher then the rear.

    The barrel is pointed well below the line of sight at the moment of ignition. Recoil moves the gun up to POA before the bullet can clear the muzzle.

    Another good example:
    Try shooting a 30-30 Winchester carbine of a bench.

    Hold it down by the forend and it will shoot where the sights are looking.

    Let go of the forearm and let it jump, and it will shoot way high.
     
  16. MrBorland

    MrBorland Moderator

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    About 0.036". You were on the right track...sort of.

    You have to solve the conservation of momentum (mass x velocity) equation, where velocity is distance per time. Time actually cancels out, since it's the same for the gun and the bullet (i.e. the amount the gun recoil while the bullet's in the barrel). The distance the bullet travels is the barrel length (L), whereas the distance the gun travels (R) is the amount of recoil you're trying to calculate. Bottom line:

    R = L x (mass of bullet*/mass of gun)

    (*maybe have to include mass of powder charge here as well)

    For a 40 oz 4" .357 mag shooting a 158 grain bullet, the gun theoretically will move about 0.036". If this muzzle movement were all in one direction, it'd send the bullet about 8" off target at 25 yards!

    Now, for some reality: This assumes the 40oz gun is hanging free in space. It doesn't generally do that, so the effective weight of the gun must include the effective weight of the shooter's body, and that of the earth they're standing on. More difficult to quantitate is how much control (via grip) the shooter has on the gun.

    Many shooters can shoot much much better than 8" groups at 25 yards, so the amount the muzzle really moves is much less than what the simple physics predicts. The simple physics does say, though, that all else being equal, a longer barrel actually increases this intrinsic recoil.
     
  17. wally

    wally Member

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    Recoil is not significant until the bullet leave the barrel with rifles and pistols. Watch any of the super slo-motion shots of guns firing that you can find on You-Tube if you don't believe me.

    Revolvers, are different since there are two "recoils", first when the bullet leaves the cylinder and enters the barrel and a larger one when the bullet exits the muzzle. So recoil during firing (before the bullet exits) does have a noticeable effect with revolvers. But any effect with rifles or pistols are swamped by changes in barrel harmonics with different loads.

    --wally.
     
  18. 1911Tuner

    1911Tuner Moderator Emeritus

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    Fascinating...

    Rather than become embroiled in yet another theory storm...Let's play "Just Imagine" and see if we can provoke thought with some sort of logical progression and conclusion.

    Being aware that perfection only exists in the mind of God, and that there is no such thing as a perfect dimension...Let's build an imaginary cannon and assume for the sake of Isaac Newton that it is indeed perfect in all described aspects.

    Let this cannon be a double-ended cannon, with a bore that is not only perfectly concentric, but also precisely the same inner diameter from one end to the other. Let's also assume that the thickness of the barrel doesn't vary even a ten millionth of an inch. The bore's surface is also precisely the same from end-to-end.

    Let's assume two identical cannon balls...both perfectly round and identical in surface finish. These two projectiles are also precisely of the same mass/weight.

    Let's place a flash hole that is located precisely in the center of the barrel, and load each ball precisely equidistant from its respective muzzle with a compressed powder charge.

    Both balls are bearing equally hard on the powder charge. Precisely and perfectly.

    Fire it.

    Will the gun recoil? If so...In which direction? If not...Why not..and what WILL happen?

    For every action, there must be an equal and opposite reaction. Equal being the operative word, here...it means equal in every way.

    E-Q-U-A-L

    I'll leave alla ya'll to wrack your brains on it and spend 3 or 4 pages on theories.

    :scrutiny:

    Popcorn, anyone? :D
     
  19. moojpg2

    moojpg2 Member

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    Wow

    come on guys, read a physics book or something


    The cannon won't recoil (defining recoil as "move"), provided 1911Tuners premise where everything is exactly the same on both sides because both shots would produce an equal and opposite force, thus producing no net force. Without force, there is no movement.

    Revolvers do not have two recoils:banghead:
     
  20. 1911Tuner

    1911Tuner Moderator Emeritus

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    Very good, mooj. You didn't quite finish it, but that's close enough. I didn't figure a ringer to come along quite this early, but since you nailed it...

    Let's use the same cannon, with everything the same as before...except the cannon balls.

    This time, let's assume that they're identical in every way...except this time...let's make one with 10X the mass/weight of the other.

    Fire it.

    What will happen?

    Will it recoil this time?

    If so...will the recoil begin at exactly the same instant that the other projectile moves...or will it "wait" until the projectile has exited its muzzle?

    If not...Why?

    Hint:

    You can't apply force in one direction, and you especially can't have force in one direction...and then later on force in the other direction...during the same action/reaction event within the same closed system, which is what would have to happen in order for the gun to sit still until the bullet exits.
     
  21. woodfiend

    woodfiend Member

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    Yeah, it seems that most of the recoil is caused by the action of the bolt, and not by the bullet travelling.
     
  22. moojpg2

    moojpg2 Member

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    Another easy one.

    I think I'll sit back and enjoy this though, It would kind of ruin it if I kept spitting out the answers.

    You kind of gave it away with the hint though.
     
  23. Loomis

    Loomis member

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    THe reason why recoil "feels" like it doesn't start until after the bullet exist the barrel is threefold:

    1) there is friction between the bullet and the barrel. THe bullet tries to drag the barrel along with it. This counteracts some of the "felt" recoil

    2) once the bullet exits the barrel, combustion gasses accelerate many times greater than the bullet ever did and add to the "felt" recoil

    3) human nervous systems aren't fast enough to perceive force, impulse, momentum, in that minute a time frame.

    oops. I just thought of one more item...

    4) In a semi auto handgun, the slide creates it's own "felt recoil" when it reverses direction and begins it's forward motion. THis happens WAAAY after the bullet it LOOONG gone.

    Conclusion: Both are correct. Recoil occurs after the bullet exits the barrel. REcoil also occurs before the bullet exits the barrel.

    And now I'll read the moderators response and see if I am duplicating anything in his post. ;)
     
  24. Loomis

    Loomis member

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    NOpe. The mod really oversimplified the theory on this one. I guess I win.
     
  25. moojpg2

    moojpg2 Member

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    No the mod didn't oversimplify anything. Once the bullet starts to move, the gun starts to move at that same instant. The movement of the gun may continue after the bullet exits the barrel due to momentum, combustion gases, and mechanical functions of the gun. The point is that recoil begins the instant the powder is ignited and the bullet begins to move.

    For every action there is an equal and opposite reaction. It doesn't get any more simple.
     
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