recoil v accuracy

[RDM416]

The only forces working to push the rifle backward at that point is the force of the bullet pressing on the air ahead of it in the barrel and the tiny fraction of hot gasses that are not contained behind the bullett.

Once the bullet clears the end of the barrel then in effect the barrel is acting like a rocket motor driving back the rifle in the opposite direction.

That is why a good muzzle brake is so effective at reducing felt recoil and muzzle flip.

Well said Wild Rose. Until the bullet leaves the barrel it is a "closed system" and the effects generated by the expanding gasses on the outside world is VERY minimal as you pointed out.

I'm just a retired electronics engineer, but we had this same discussion on here a couple of years ago. A couple of guys who are real physicists weighed in on the subject and explained the closed loop system of of a rifle barrel / bullet. I think the orginal question then revolved around if there was any difference in velocity between a bullet fired from a tightly held rifle or one allowed to "free recoil". Different question, but the real world physics is still the same.

The bullet is GONE before recoil starts to push the rifle around.

 

[SBruce]

OK, I can maybe buy into the rearward recoil being minimal untill the bullet is gone or nearly gone, but I am visualizing torque as being totally different.

I would think that as soon as the bullet engages the rifleing, then the equal and opposite effect begins and the rifle tries to torque counter clockwise (looking from the rear).

No matter if it's torque or rearward movement or rearward movement caused by reactive torque (a screw type effect if you will), the rifle is in fact moving some before the bullet leaves the barrel............Makes the most logical sense to me anyway.

 

[WildRose]

OK, I can maybe buy into the rearward recoil being minimal untill the bullet is gone or nearly gone, but I am visualizing torque as being totally different.

I would think that as soon as the bullet engages the rifleing, then the equal and opposite effect begins and the rifle tries to torque counter clockwise (looking from the rear).

No matter if it's torque or rearward movement or rearward movement caused by reactive torque (a screw type effect if you will), the rifle is in fact moving some before the bullet leaves the barrel............Makes the most logical sense to me anyway.

No, torsion is restricted by the same principles of physics.

Until the bullet exits, all the forces are acting on the bullet itself.

The torquing effect is felt because the gasses escaping the barrel are following the path created by the lans and grooves of the rifling creating a vortex of gasses at the barrel as they exit.

As long as the pressure vessel remains sealed, the forces are simply driving forward. Energy always seeks the path of least resistance, and twisting a small bullet is far easier than twisting a rifle that out weighs it by many, many times over.

Again, with a proper muzzle brake you will notice little to no torque effect at all.

 

[coonhunter]

If recoil does not begin until after the bullet leaves the barrel then why does how you hold the rifle matter at all?

You have a bullet of some mass accelerating from 0 to 3000 fps. As soon as that bullet begins to accelerate Thare is an oppsite and equal reaction. The initial action is the expansion of the gasses from the burning powder, the equal reaction is the bullet accelerating forward, and the oppsite reaction is the rifle moving backward.

 

[WildRose]

If recoil does not begin until after the bullet leaves the barrel then why does how you hold the rifle matter at all?

You have a bullet of some mass accelerating from 0 to 3000 fps. As soon as that bullet begins to accelerate Thare is an oppsite and equal reaction. The initial action is the expansion of the gasses from the burning powder, the equal reaction is the bullet accelerating forward, and the oppsite reaction is the rifle moving backward.

Until the pressure of the expanding gas exits the barrel that equal and opposite reaction is contained within the pressure vessel.

The only force exerted ahead of the bullet are the air pressure (environmental as in barometer) and the tiny fraction of gas that gets around the bullet. Thus there is nothing to push the rifle back other than a tiny, tiny amount of air pressure.

Notice in this video when the recoil shows it's effect.

[ame="http://www.youtube.com/watch?v=BW93WQ98s-I"]Gun shot so slow you can see the bullet - YouTube[/ame]

The main reason it matters how you hold the rifle is to get properly alinged and steady on target, keep yourself from flinching, reduce felt recoil against your shoulder and to remain closer to on target so you can see your bullet impact and make quicker follow up shots.

With a decent muzzle brake you can set your rife on a bipod and the butt sitting on sand bags and fire a nice tight group with only your finger in the trigger and no other contact point against your body.

 

[budlight]

Well said Wild Rose. Until the bullet leaves the barrel it is a "closed system" and the effects generated by the expanding gasses on the outside world is VERY minimal as you pointed out.

I'm just a retired electronics engineer, but we had this same discussion on here a couple of years ago. A couple of guys who are real physicists weighed in on the subject and explained the closed loop system of of a rifle barrel / bullet. I think the orginal question then revolved around if there was any difference in velocity between a bullet fired from a tightly held rifle or one allowed to "free recoil". Different question, but the real world physics is still the same.

The bullet is GONE before recoil starts to push the rifle around.

I don't care when you think recoil starts. I said that the equal and opposite reaction starts when the bullet moves the first micron. It is really stupid to think that moving an object doesn't require force because it is inside a pipe. If your idea was correct my semi auto 12 gauge and pistols would not work. They are spring actions - not gas operated. The action starts to come back as soon as the bullets or shot moves.

 

[RDM416]

Budlight,

I understand it does not seem follow the "equal and opposite" reaction law of physics, but it does. In order to understand the principal that "Wild Rose" brought up, you have to know what a "closed loop system" is in physics.

Until SOMETHING moves external to the barrel, the bullet, barrel, case......... are in a closed loop. When the bullet leaves the barrel, the closed loop is OPENED and all the recoil factors begin. As Wild Rose pointed out there is a tiny amount of air in the bore that is being pushed out the end of the bore in front of the bullet and there would be the tiny amount of expansion of the barrel steel. Those are EXTERNAL and keep the system from being a total "closed loop", however the effect of those things are so small as to not matter.

It has been 30 years since college physics for me so I am a little rusty here, but if you are interested in understanding, look up "closed loop systems" in a physics text.

After all that........ I will still maintain my statement that the recoil of the rifle does not affect it's accuracy, only how we react to it.

It's been fun, and a good discussion, and will admit I certainly could be wrong. Not trying to be the resident physics expert here because I'm not.

 

[WildRose]

I don't care when you think recoil starts. I said that the equal and opposite reaction starts when the bullet moves the first micron. It is really stupid to think that moving an object doesn't require force because it is inside a pipe. If your idea was correct my semi auto 12 gauge and pistols would not work. They are spring actions - not gas operated. The action starts to come back as soon as the bullets or shot moves.

In a semi auto the "equal and opposite reaction" is not retained within the pressure vessel until the bullet/wad exits.

The pressure vessel releases the hot gases as soon as the action cycles.

That is not the case with a closed, locked bolt.

The equal and opposite reaction in a closed system/pressure vessel contains the forces which are pressing outward, equally in all directions until the muzzle is cleared, thus there is no observable or felt recoil until the bullet exits.

See the video linked to above for a demonstration.

 

[Boss Hoss]

I like it when people who know what the devil they are talking about make valid points!

 

[Buffalobob]

I just don't think I am in the mood for arguing this.

A rifle barrel is not a closed loop system.

Start with basic physics or Statics depending on your training F = m d2x/dt2. If you violate this law then you are wrong.

Then apply conservation of momentum which says M1= M2 where M = mdx/dt.

If you violate this law you are wrong.

There is a reason rockets can accelerate and decelerate in a vacuum.

For those who can remember what the value of inertial frames are, run the calculations with one frame with the bullet stationary, another one with the rifle stationary and then one where both are allowed to move.

The action starts to come back as soon as the bullets or shot moves.

If this was not true, then the mass of air in a shotgun barrel would have to be equal to the mass of the bolt. This would be some pretty dam heavy air even for this website.

the forces which are pressing outward, equally in all directions until the muzzle is cleared,

This is untrue. Prepare a simply vector diagram of the forces and it becomes obvious. Alternatively calculate the mass of air that you say is causing the recoil and see what the density of your air has to be.

 

[WildRose]

I just don't think I am in the mood for arguing this.

A rifle barrel is not a closed loop system.

Start with basic physics or Statics depending on your training F = m d2x/dt2. If you violate this law then you are wrong.

Then apply conservation of momentum which says M1= M2 where M = mdx/dt.

If you violate this law you are wrong.

There is a reason rockets can accelerate and decelerate in a vacuum.

Yes it's because the expanding hot gasses are shooting out of it's *** driving it forward. This does not happen until the thrust generated by said hot gasses exceeds the mass of the rocket.

This does not occur with a rifle until the bullet exits the barrel. Only a tiny amount of gas escapes around the bullet and exits ahead of it. The mass and pressure of air ahead of the bullet has no measurable effect in driving the weapon in the opposite direction.

For those who can remember what the value of inertial frames are, run the calculations with one frame with the bullet stationary, another one with the rifle stationary and then one where both are allowed to move.

Inertia does not apply to the actions within the closed pressure vessel which is the barrel capped on one end by the bolt and the other by the bullet. The only intertia involved is in driving the bullet forward within the barrel at this point. There is nothing to exert force to your shoulder as in recoil.

The forces between the bullet and the bolt are exerting equal pressures in all directions and there is no force acting to push the gun backwards until those hot gasses and bullet exit from the barrel.

This is untrue. Prepare a simply vector diagram of the forces and it becomes obvious. Alternatively calculate the mass of air that you say is causing the recoil and see what the density of your air has to be.

There is no mass of air causing recoil. What causes recoil is the compressed gas that is driving the bullett forward. Once the bullet clears the barrel, the force that was driving it out of the barrel is released and acts just like a rocket motor driving the rifle backwards.

Again, look at the video.

Again, this is why a well made muzzle brake is able to reduce recoil and muzzle flip dramatically.

 

[lightwind]

OK, I have to join in on this discussion. First, the gun does not have to move backward to affect the bullet motion. I won't go into that in this post because I have not gone through my version of the math (and might not get to it today). However, I have looked at what the barrel does. Remember that the barrel rings like a bell and has multiple modes of vibration. The issue (and the reason some loads are better than others) is that you try to get the bullet out at a consistent location of the vibration of the barrel. As an example, when the bullet fires and connects with the lands it sends a shock wave through the barrel (not recoil but a shock wave). The shock wave moves at the speed of sound in steel through the barrel (about 3000 meter/sec or about 19,685 ft/sec). If we use the time in the barrel (about 2ms) from RDM416 we get about 10 cycles up and down the barrel for the shock wave before the bullet clears the barrel (just a quick estimate). What that means is that the barrel starts vibrating very quickly after detonation. This is one of the reasons that a heavy barrel is better than a light barrel and barrel stiffness is important. I am in agreement that the gun does not move much (although I have not done the calculations it is just common sense) but the barrel starts reacting from the moment of the primer detonation. Tuning the vibration of the barrel to the load is one of the more important parts of precision (not accuracy). In the case of the shooter here - I assume that he has tried multiple loads to be sure that it is not the load affecting his precision. However, tuning a heavy load becomes more important as the barrel stiffness goes down.

 

[WildRose]

OK, I have to join in on this discussion. First, the gun does not have to move backward to affect the bullet motion. I won't go into that in this post because I have not gone through my version of the math (and might not get to it today). However, I have looked at what the barrel does. Remember that the barrel rings like a bell and has multiple modes of vibration. The issue (and the reason some loads are better than others) is that you try to get the bullet out at a consistent location of the vibration of the barrel. As an example, when the bullet fires and connects with the lands it sends a shock wave through the barrel (not recoil but a shock wave). The shock wave moves at the speed of sound in steel through the barrel (about 3000 meter/sec or about 19,685 ft/sec). If we use the time in the barrel (about 2ms) from RDM416 we get about 10 cycles up and down the barrel for the shock wave before the bullet clears the barrel (just a quick estimate). What that means is that the barrel starts vibrating very quickly after detonation. This is one of the reasons that a heavy barrel is better than a light barrel and barrel stiffness is important. I am in agreement that the gun does not move much (although I have not done the calculations it is just common sense) but the barrel starts reacting from the moment of the primer detonation. Tuning the vibration of the barrel to the load is one of the more important parts of precision (not accuracy). In the case of the shooter here - I assume that he has tried multiple loads to be sure that it is not the load affecting his precision. However, tuning a heavy load becomes more important as the barrel stiffness goes down.

The speed of sound is 1,126 feet per second, not 19,685fps.

 

[lightwind]

"The speed of sound is 1,126 feet per second, not 19,685fps."

No, you are assuming that the speed of sound is the same in air (a compressible medium) as in liquids or solids. That is a very poor assumption. Please go look up the speed of sound in steel and get back to me.