recoil v accuracy

[WildRose]

"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.

**** me for skimming!

Should have read the whole thing.

Yes sound waves travel about 4x faster in water and 15x faster through solids like steel.

 

[Boss Hoss]

Ahhhhhhh but everyone knows the answer and it is in fact exactly 20 times the speed of an unladed swallow!!

 

[Buffalobob]

I went outside and poured a whole beer into bowls to see if I could drown the slugs eating my tomatoes.

 

[RDM416]

I went outside and poured a whole beer into bowls to see if I could drown the slugs eating my tomatoes.

I knew if we kept this thread going long enough we could get Buffalobob to come out and play

Maybe not a complete closed loop, however let me offer this example.

Take a steel pipe and put a high pressure fitting on one end and a stopper in the other end...... The pipe will not move "recoil" until the pressure rises to the point required to blow out the stopper. The pipe may swell, but there will be NO rearward recoil until the pressure is released.

If the stopper is placed at the bottom end of the pipe near the high pressure fitting and the pipe is pressurized at some point the pressure will rise to the point to the point to begin pushing the stopper out the pipe. At that point the pressure is pushing against the "stopper" and the end of the pipe, so the the loop is still "closed". Where the "stopper" is in the pipe makes no difference

I will agree that as the stopper moves the length of the pipe there will be vibrations caused by it passing the length of the pipe....... vibration, not not rearward recoil.

Just think of it this way. If you pressurize an air cylinder NOTHING moves "recoils" until the pressure is released, otherwise when you filled an air tank it would keep trying to jump away from the point where the air is being introduced.

Keep in mind as well that in a rifle barrel or any pressurized cylinder that the pressure is the SAME EVERYWHERE, at the base of the bullet pushing forward, along the bore pushing outward and at the chamber pushing back...... pressure is EQUAL. Equal pressure means everything cancels, just like a pressurized air cylinder don't jump around.

I thought I was done with this one on my last post but I just couldn't help myself
It may have been better keep my mouth shut and not "remove all doubt" about my lack of physics expertise, but it is more fun to argue.

 

[lightwind]

RDM416: Nope. You are thinking of the barrel and bullet as being a closed system. It is not. The law is that force = acceleration*mass. f=m*a. In this case the acceleration is of the bullet and gas through the barrel. The equal and opposite force is against the bolt face. The forces normal to the diameter of the barrel cancel out so there is no sidewise force. The result is that the bolt face is subject to the same backward force as the bullet is forward. The differences in acceleration is due to the differences in the mass. As one of the earlier posters pointed out, that is how recoil operated actions work. If things worked as you say and there was no net force transmitted until the bullet left the barrel the bolt face would not have any force against it because at that point the gas is escaping and pressure is rapidly dropping. So, as the bullet feels the force pushing it forward, there is an equal and opposite force acting on the gun through the bolt face. Think about it for a while and let me know where you think this is wrong. Also think about assuming that this is a closed system when the bullet is moving with only friction and air pressure (external forces) acting on it.

 

[WildRose]

RDM416: Nope. You are thinking of the barrel and bullet as being a closed system. It is not. The law is that force = acceleration*mass. f=m*a. In this case the acceleration is of the bullet and gas through the barrel. The equal and opposite force is against the bolt face. The forces normal to the diameter of the barrel cancel out so there is no sidewise force. The result is that the bolt face is subject to the same backward force as the bullet is forward. The differences in acceleration is due to the differences in the mass. As one of the earlier posters pointed out, that is how recoil operated actions work. If things worked as you say and there was no net force transmitted until the bullet left the barrel the bolt face would not have any force against it because at that point the gas is escaping and pressure is rapidly dropping. So, as the bullet feels the force pushing it forward, there is an equal and opposite force acting on the gun through the bolt face. Think about it for a while and let me know where you think this is wrong. Also think about assuming that this is a closed system when the bullet is moving with only friction and air pressure (external forces) acting on it.

The pressure exerted against the bolt face is retained until the bullet exits the barrel.

There is no thrust generated against the rifle itself propelling it backwards until that point in time.

As long as the pressure remians contained within the barrel, no recoil is possible.

Recoil works like a rocket engine. No thrust can drive the rocket forward until it is releases from the rocket motor, or from compressed gases being released via valves.

Until the bullet exits, it IS a closed pressurized container other than the minute amount of leakage that gets around the bullet which is not significant enough to cause any percieved recoil effect.

Again everyone, please, look at the video I posted again. It demonstrates these principles very clearly.

 

[lightwind]

http://www.longrangehunting.com/forums/members/rdm416/: Wow. All your video shows is a slowmo of the bullet and the gun. It does not do a good job of showing the gun accelerate while the bullet is in it. Let me give you another perspective on the system. What has happened is that there is an "impulse" on both the bullet and the gun (with the hand). One of the laws that is involved is momentum. In this system momentum is conserved. Energy is conserved but changes forms from motion to a combination of motion and heat and is more difficult to keep track of.

Since momentum is conserved we can use those equations of motion to see that the center of mass of the system stays the same. In the beginning the total momentum of the system was zero and after the impulse (integral of force over time) the momentum is still zero with the bullet moving forward and the gun moving backwards. In the video the initial impulse is not clear since the gun and hand are accelerating much slower than the bullet (because they weigh more).

You are right about the gun going back being similar to a rocket going forward because the same rules apply. However, what you don't seem to understand is that the rocket starts being accelerated by the force of the propellant as it is accelerated starting at zero motion. It is not accelerated just by the gas leaving the rocket, it is accelerated the whole time the gas is accelerated.

You use the example of the muzzle brake. What happens is that at the end of the barrel the direction of the gas is changed which applies a force to the gas and to the gun simultaneously mitigating the recoil that the mass of gas escaping through the muzzle would have taken with it.

Please let me know what is not clear in this explanation because I would like to clear this up.

 

[WildRose]

: Wow. All your video shows is a slowmo of the bullet and the gun. It does not do a good job of showing the gun accelerate while the bullet is in it. Let me give you another perspective on the system. What has happened is that there is an "impulse" on both the bullet and the gun (with the hand). One of the laws that is involved is momentum. In this system momentum is conserved. Energy is conserved but changes forms from motion to a combination of motion and heat and is more difficult to keep track of.

Since momentum is conserved we can use those equations of motion to see that the center of mass of the system stays the same. In the beginning the total momentum of the system was zero and after the impulse (integral of force over time) the momentum is still zero with the bullet moving forward and the gun moving backwards. In the video the initial impulse is not clear since the gun and hand are accelerating much slower than the bullet (because they weigh more).

You are right about the gun going back being similar to a rocket going forward because the same rules apply. However, what you don't seem to understand is that the rocket starts being accelerated by the force of the propellant as it is accelerated starting at zero motion. It is not accelerated just by the gas leaving the rocket, it is accelerated the whole time the gas is accelerated.

The rocket does not accelerate until the forces contained are released.

The recoil does not begin, until the forces contained are released.

You use the example of the muzzle brake. What happens is that at the end of the barrel the direction of the gas is changed which applies a force to the gas and to the gun simultaneously mitigating the recoil that the mass of gas escaping through the muzzle would have taken with it.

No, the muzzle brake redirects the flow of the gases much like the nozzles on the Harrier do. When the nozzles rotate downward the thrust is downward lifting the plane. When the nozzles are rotated backwards they thrust the plane forward.

There IS NO THRUST coming from the gun barrel to force the weapon backwards until the bullet and gases escape the barrel.

As for the video it shows no recoil until the bullet and gases leave the barrel because that's how it works. In order to produce a rearward thrust of the weapon there must be a force acting to drive it backwards.

Energy contained within the barrel while plugged at one end by the bullet and at the other by the bolt cannot propel the weapon in any direction because those forces are contained.

 

[WildRose]

I'm done with this. Hopefully the Op's questiona have been answered and some of the others new to the sport learned something.

I have learned over the years that some people are simply too smart to learn anything.

 

[lightwind]

As usual I can't describe things as well as some of those who have been around a longer time. My background is physics and that can make some of my descriptions uninteligable. So, I went back to the archives here to see what some of the better versed had to say. Here is an article in the archive that is well worth reading:

Dwell Time And Your Trigger

As you can see, he says the rifle recoils about 0.25 to 0.375 inches before the bullet leaves the rifle.

Here is the thread that led to this article.

http://www.longrangehunting.com/forums/f17/does-recoil-efect-accuracy-52967/

Here is a physics site that the thread points to:

The Physics of Everyday Stuff - Gun Recoil

The physics thread includes both of our points and shows how momentum is conserved AND how the gas escaping gives a second acceleration. I think this sums it up pretty well.

 

[lightwind]

I'm done with this. Hopefully the Op's questiona have been answered and some of the others new to the sport learned something.

I have learned over the years that some people are simply too smart to learn anything.

I'm glad you have learned it all. What do you think of the last post or are you ready to argue with everyone out there that the gun does not move until the bullet leaves the barrel? I have learned something from the research for this - but I guess I learned it wrong since it does not agree with your view of the world. Sorry, but the gun moves as the bullet and powder move.

 

[WildRose]

I'm glad you have learned it all. What do you think of the last post or are you ready to argue with everyone out there that the gun does not move until the bullet leaves the barrel? I have learned something from the research for this - but I guess I learned it wrong since it does not agree with your view of the world. Sorry, but the gun moves as the bullet and powder move.

I haven't "learned it all". I have howerver learned as much as there is to be known on this particular subject.

There is no significant recoil effect that is felt or observed until the bullet and gases escape the pressure vessel. At that time the rifle acts like a rocket motor and is driven backwards.

The inertial effects that occur while the round is still in the barrel are extremely minimal, and not enough to affect accuracy significantly if the gun is being held at all.

With a decent muzzle brake you can set a rifle on the bench resting solely on a bipod and sandbag pulling the trigger with one finger only and hit the target.

You have an 8 lbs rifle which outweighs the moving projectile by many orders of magnitude so the inertial effect is near zero on the rifle. The Mass of the bullet vs the mass of the entire rifle is not significant enough to have any substantial effect on recoil and accuracy as long as the bullet remains in the barrel.

 

[lightwind]

Just so that people are not confused by your comments:

Your comment: "The rocket does not accelerate until the forces contained are released."

No, that is not true. The rocket accelerates as the propellant is accelerated.

Your comment: "The recoil does not begin, until the forces contained are released."

No, that is not true. No, it begins as the momentum of the bullet starts changing at the time of ignition.

It is difficult to reconstruct the past when it you have put it in writing.

 

[MT4XFore]

Why is it then that one's garden hose doesn't recoil until you squeeze the trigger on the nozzle and the water comes out?