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Gun Recoil vs POI

34K views 202 replies 27 participants last post by  LIKTOSHOOT 
#1 · (Edited)
This is technical information that I knew was correct but have been debating it unconvincingly for years. Now I've finally found a physicist to confirm it!

An assertion made by a YouTuber I'm subscribed to.

I believe POI is changed by recoil impulse. I know that some of my hotter loads print left of the lighter weight and slower shooting loads. In my 45-70 at 50 yards my slower loads print much higher - I assume this is because the recoil has already started to take effect before it leaves the barrel as it is rising. That is my theory.
My response.

Barrel harmonics notwithstanding... I have seen a higher vertical POI difference when shooting subsonic bullets as opposed to supersonic. I attribute the faster bullet's lower POI to the "bullet bow shock-wave."

With bullets traveling in the same velocity categories, (subsonic, transonic, supersonic,) I find faster bullets hit higher.

In my favorites I have videos of slow motion firearm shooting. Recoil, (barrel climb,) happens only after the bullet has left the barrel.

"The velocity of a body remains constant unless the body is acted upon by an external force." --Newton.

The bullet and pressurized gasses while in the barrel, are a part of a self contained, (internal,) pressure vessel. After the bullet is expelled, and subsequently the pressure, the gasses no longer contained within, become an external force.
Here is where you can find the scientific version.
The Physics of Everyday Stuff, Gun Recoil: by Sam Hokin, physicist

Here is a bit of the information, please visit the page for the whole article, it is easy to understand.

Summary
  1. The total momentum of a system is conserved if there are no outside forces acting on it.
  2. Gun recoil results from conservation of total momentum of the bullet-gun system: the backward recoil gun momentum balances the forward bullet momentum to maintain zero total momentum.
  3. Gun recoil actually has two parts: primary recoil from the escaping bullet and secondary recoil from the escaping gas behind the bullet.

I want to make sure this part is stressed.
However, if you look at a bullet and gun together (say while the bullet is still in the barrel but already heading out at full speed), you can say there is no net force on the bullet-gun system.
My "pressure vessel" is his "bullet-gun system;" it is exactly the same principle. When they are together as one, there is "zero total momentum."

Now I can rest easy and send people here for the explanation!

I also want to show what "bullet bow shock-wave" is.
The same thing you see as a bullet travels through the air... as in my latest video.
Winter Load, 400 Yards, At 50 Degrees
You just cant see it defined like the above video.
 
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#184 ·
I will always go with the laws of physics and if something doesn't appear to follow them then I figure I am not seeing something. There is no reaction in a closed system unless acted on by an outside force. When the bullet is fired the pressure chamber is expanding but all forces are equal in all directions. The bullet is actually pushing the gun forward due to friction and turning the rifle due to torque created by the rifling twist. In a revolver where the gases begin escaping between the cylinder and barrel the reaction begins while the bullet is in the barrel. With an auto loader the slide begins to actuate while the bullet is in the barrel and change begins. The shooter is adding an external force component by pulling the trigger. If it is a 4# trigger pull then there is a 4# load applied and then suddenly removed when the hammer falls. It makes sense that a slower bullet is in the barrel longer so would have a greater change in error but the recoil effect in a bolt gun comes after the bullet exits the barrel. I don't think you can say the cause for the change in the point of impact is because of the slower bullet but that the external forces are easier seen with a slower bullet.
 
#185 ·
I'm showing up a bit late to the party here but ill surmise my understanding of the opening post.

The bullet moving inside barrel and all pressure involved have a very minute effect on recoil. Much the same way a grown man doesn't exert much force to throw the same bullet by hand. Recoil comes from the high pressure and speed of gases exiting muzzle. If a guy had a powder that produced 1000 psi but pushed a 100gr bullet at 3500fps he would feel very, very little recoil.

I've read somewhere the gasses travel about 5 times as fast as the bullet. Any truth to that?
 
#186 ·
Here's a thought about why revolver sights line up horizontally while the barrel points downward;
The recoil starts as soon as the bullet leaves the cylinder. So, by the time the bullet leaves the barrel, the recoil has brought the barrel into a position to compensate for the recoil.
 
#188 ·
You are entirely correct, Grizzley1. The instant the primer fires, a building force within the cartridge caused by expanding gasses from the combustion of the powder accelerates the bullet along the axis of the barrel of the gun. This force is resisted by a reaction force applied by the hand holding the weapon. Since the barrel lies above the plane of the hand holding the gun, a rotational component called a 'moment' exists which tends to lift the muzzle by inducing rotation around the axis defined by the intersection of the line of the barrel and the line downward through the hand perpendicular to the barrel. It is difficult, if not impossible, to correlate the amount of upward deflection to the weight of the bullet, as there are so many other variables involved. In simple terms, as the OP mentioned, total energy of the system is always conserved, but the energy released during the firing of a cartridge is extremely difficult to determine.

Interesting discussion, to say the least!:D
What!!!!! When a non-engineer asks you if you want a cup of coffee, do you respond in such a way you actually get a cup of coffee, or are they (me) still waiting for the answer? Glad you Inga-neers do what you do and I don't have to understand, or I'd still be using bark scoopers and leaves!!!!!:D
 
#190 ·
Been a while since this thread was visited but it's worthy of being bumped up.

While wandering aimlessly on you tube I ran across a new video showing some guns being fired in super slow motion, 100,000 frames per second. Pay close attention to the AK 47 and the Barrett .416, you will plainly see the guns moving under recoil before the round exits the bore, it's also plain to see the slide on the 1911 moving before the bullet exits the bore.

 
#191 ·
Hold you revolver limp wristed and see if the bullets go where you want them to. For every action there is an equal and opposite reaction. The very instant the bullet starts traveling in one direction the gun starts to go in the other direction.
 
#192 ·
If you remove the operator input, at the point of ignition, it is a closed system and forces are equal in all directions so there is no recoil. There is a torque from the twist of the rifling. When the bullet leaves the barrel the forces become unequal and the recoil happens. POI is affected by the operator not the recoil. If POI was affected by recoil you would need to sight a .22 a lot higher than a 458 win mag. Iron sights on rifle barrels are calibrated by the caliber drop, not by how much recoil there is. A sporting barrel and a bull barrel have the same sights even though the bull barrel has less recoil because of the weight.
 
#194 ·
I will have to respectfully disagree, a rifle or pistol is not a closed system, the bullet is free to move and so is the gun, barring any resistance by the shooter's body. If the bullet is capable of being moved by the force of the expanding gas, so is the gun.
 
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#196 ·
On a rifle, if the case seals and the bullet seals it is a closed system and even though he bullet is moving the volume only changes. The reaction is from the rifling and the force difference on the area of the bullet vs the area of the case base that cause the reaction. The dwell time videos of a pistol are correct because the reaction begins when the system opens and on a revolver it is when the bullet leaves the cylinder and enters the barrel by the escaping gases between the cylinder and breech. In that case, the longer the barrel, the longer the change in muzzle position affects the POI. On the AK you can see the gasses acting on the muzzle break forcing the barrel down, not up.
 
#197 ·
WOW, this thread has gone on for SIX YEARS. A slow-motion video will show you that the projectile leaves the end of the barrel BEFORE the barrel moves in recoil. Now, what is the question?
 
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#203 ·
Me too.....me too!!

Back in my rimfire addiction this was the biggest bunch of BS running. Barrel length.
And then was born the 16" HB as the cure and the debate began; first was the velocity issue......longer barrels slowed down the bullet and caused flyers as the amount of shots fired would foul the barrel a little and there inlayed the beginning.

Shorter barrels allowed for quick exit of bullet and shorter bull barrels had less whip if any in the rimfire because they were short and "stiffer."

I shot 24-26" barrels and never found that to be the case. One of the biggest killers of these so called experts was not the barrel, and I found out just by doing some light research there was a very large issue at hand and it was not the barrel.

A term way back that I had never really thought of or had really heard of; "Lock Time"
In my custom (2) built Ruger VMBZ`s it showed up once I knew what it was.
I changed the "Striker Spring" from factory to (Blitzschnell) 23LBS. While not done in a controlled environment it changed two rifles, one a factory barreled .22Mag VMBZ 24" barrel and the other a full out in .17HMR with a GM barrel 20" plus my barrel treatment to both(too long for here)


Even though I had reworked the actions for headspace the 23lbs spring was the end play.

I posted that target here years back and it created a firestorm........didn`t care.
Never found any brand of rifle to beat it and it caused several of my friends to dump their Anshultz and that's nothing against them.

If I can`t find the target here I believe I still have some in my books showing such.
100yrd 5 shot group about the size of this:)
It was not a fluke as I have many and the .22 mag just a little larger.

Barrel whip can effect lightweight barrels, but I never had that problem on my Model 70 Super Bull single shot in 300WM, granted I think that barrel was 1" or 1-1/8" in diameter.
 
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