recoil v accuracy

[WildRose]

Nope. The external force (external to the bullet, which is precisely the thing we want "acted on"! Not the barrel !) happens to be the powder pressure behind the bullet which overcomes the atmospheric pressure in front of the bullet. The barrel does not "contain" the pressure "in all directions", it only directs it towards the target. Otherwise the entire concept of shooting would be bogus. And of course the pressure is decaying as the bullet proceeds down the barrel. The powder transfers about 34% of its calorific value into producing hot gas which propel the bullet and about 70% of that energy becomes the bullets kinetic energy. The remaining 30% of the original 34% (about 10% of the original powder energy) is expended as muzzle blast unless the barrel is too short.

Incorrect, pressure continues to build as long as it is constrained by the bullett and it is still burning.

The gas continues to expand and create pressure as long as there is combustion and a pressure vessel.

Again, this is why a good muzzle brake can eliminate most felt recoil.

 

[WildRose]

... . The barrel does not "contain" the pressure "in all directions", it only directs it towards the target.

Sorry but this is gibberish. If the bolt, brass and barrel did not constrain the force of the blast it would be impossible to then predictably direct the bullet on the chosen path. We'd be talking about shrapnel rather than projectile at that point.

The purpose of the barrel, chamber, brass, is to trap as much of the pressure as possible and direct it in a specific direction.

Otherwise the entire concept of shooting would be bogus. And of course the pressure is decaying as the bullet proceeds down the barrel. The powder transfers about 34% of its calorific value into producing hot gas which propel the bullet and about 70% of that energy becomes the bullets kinetic energy. The remaining 30% of the original 34% (about 10% of the original powder energy) is expended as muzzle blast unless the barrel is too short.

No the pressure continues to build as the bullet travels down the barrel as long as combustion is still taking place.

That is why for precision long range shooting, we tend to use longer barrels and slower burning powders so as to keep the pressure building slower over a longer period of time vs, faster burning powders that are more rapidly consumed. This keeps temperatures down along with maximum pressure while giving us peak accuracy/velocity in combination.

 

[bman73]

This was a finite element analysis run on a rifle action/barrel to understand what was going on. All the deformations are magnified many times so that even a layman can see what is going on. Varmint Al is a retired engineer.

Extract
"CONCLUSION.... Maybe the "consensus" was that a rifle barrel vibrated in one or more of the mode shapes when fired. That was because the mode shapes and frequencies were easy to calculate and they did seem to answer some of the questions. From these FEA dynamic pressure calculations, it appears that the recoil and forced deformations are much more important than the natural vibration modes in determining where a barrel is pointing when the bullet exits the muzzle. Then after the bullet exits the muzzle, the rifle barrel vibrates in its various natural frequencies and mode shapes. Put another way, consider a guitar string being plucked. One pulls the string into a position (forced position) then releases it and the string vibrates at is natural frequency. The recoil and bullet motions "pulls" the rifle barrel to a new shape and once the bullet leaves the barrel, then the barrel vibrates. However, the addition of the scope to the model has shown some small high frequency vibrations superimposed on the forced deformations, both of which, slightly alter where the muzzle points before the bullet exits. For lowering the amplitude of the high frequency vibrations, it appears that even an "out of tune" tuner is better than no tuner at all. "

You can read his engineering page here: Varmint Al's Engineering Page - Finite Element Analysis of Structures

"Before retiring in 1990, I worked at the Lawrence Livermore National Lab for 30 years. The last few years I was the Advanced Engineering Analysis Group Leader in Weapons Engineering Division. We analyzed very complex structures. Physics developed the concepts and engineering made them deliverable. It was a great job and it was rewarding to help win the Cold War. Before becoming group leader, the last weapon system I worked on was the B-83."

Read the original article here : Barrel Harmonics Mode Shape Movies

Final addition:

Here the force on the butt and fore end of the rifle were measured when weighed down with sandbags. This data fully refutes the claim that recoil begins when the bullet reaches the muzzle.

Note the force on the butt peak at about 112lb at about 0.6ms, long before the bullet has reached the muzzle. The fore end has lifted off the rest (was loaded 10lb) even before that.

Think that this graph pretty much puts an end to this one, my next step was to send a letter to Mythbusters and get them to test it, cause you just know that they are gonna blow something up spectacularly

 

[westcliffe01]

Would you like to tell us what line of work you are in ? And how you are qualified to discredit the evidence provided ? Did you run any experiments of your own, take measurements, graph results etc ?

The guy who ran the FEA analysis and compared to shooting results has impeccable credentials. And the shooter he worked with was involved in competitive shooting. I suppose it is all just a hoax and the earth is probably flat too ?

You sir, dispute the credibility of some of the best shooters in the industry like David Tubb who was the shooter who said that he removes the over travel screw from his match trigger. Now you dispute the work of one of the foremost nuclear munitions experts, being Varmint Al.

I am a mere engineer, yet the explanations I gave you are covered in high school physics. That you should dispute such basic concepts is pretty sad. But please: Enlighten us to your superior knowledge...

Sorry but this is gibberish. If the bolt, brass and barrel did not constrain the force of the blast it would be impossible to then predictably direct the bullet on the chose path. We'd be talking about shrapnel rather than projectile at that point.

The purpose of the barrel, chamber, brass, is to trap as much of the pressure as possible and direct it in a specific direction.


No the pressure continues to build as the bullet travels down the barrel as long as combustion is still taking place.

That is why for precision long range shooting, we tend to use longer barrels and slower burning powders so as to keep the pressure building slower over a longer period of time vs, faster burning powders that are more rapidly consumed. This keeps temperatures down along with maximum pressure while giving us peak accuracy/velocity in combination.

 

[WildRose]

Think that this graph pretty much puts an end to this one, my next step was to send a letter to Mythbusters and get them to test it, cause you just know that they are gonna blow something up spectacularly

No your graph puts an end to nothing. It calls into great question the set up of the experiment.

It shows all recoil forces at zero when the bullet exits the chamber.

Again, this is impossible or muzzle brakes could not reduce felt recoil.

 

[WildRose]

Would you like to tell us what line of work you are in ?

Today? I'm a guide, outfitter trainer and breeder of birddogs. In the off season I do a lot of things including teaching both practical and personal defense shooting.

I also have 12 years experience shooting bad guys at very long range. I grew up shooting prairie dogs open sight first with a .22lr, and then with a 7mm Rem 700bdl. I never shot a scoped rifle until after joining the service.

And how you are qualified to discredit the evidence provided ?

40 years of experience with everything from handguns to heavy artillery.

Did you run any experiments of your own, take measurements, graph results etc ?

Thousands.

The guy who ran the FEA analysis and compared to shooting results has impeccable credentials. And the shooter he worked with was involved in competitive shooting. I suppose it is all just a hoax and the earth is probably flat too ?

Goody for him. I've spent forty years killing people and critters at very long range with a variety of weapons.

You sir, dispute the credibility of some of the best shooters in the industry like David Tubb who was the shooter who said that he removes the over travel screw from his match trigger. Now you dispute the work of one of the foremost nuclear munitions experts, being Varmint Al.

No sir, anytime Al wants to lecture me on nuclear weapons I will be more than happy to defer to his expertise. We're not talking nuclear weapons here but firearms.

I am a mere engineer, yet the explanations I gave you are covered in high school physics. That you should dispute such basic concepts is pretty sad. But please: Enlighten us to your superior knowledge...

One of the key aspects of good science is observation of experiments, noting the results, and coming to cause/effect conclusions.

Try shooting your favorite big magnum without a good muzzle brake.

Then shoot it with a good muzzle brake.

Then let us know which had the most felt recoil.

 

[westcliffe01]

Some people who shoot 6mm rifles (particularly 14lb benchrest ones) would claim that they have near zero recoil. That was certainly my opinion shooting the 5.56 round in the heavy Galil select fire rifles when I was in the armed forces.

No you graph puts an end to nothing. It calls into great question the set up of the experiment.

It shows all recoil forces at zero when the bullet exits the chamber.

Again, this is impossible or muzzle brakes could not reduce felt recoil.

 

[WildRose]

Some people who shoot 6mm rifles (particularly 14lb benchrest ones) would claim that they have near zero recoil. That was certainly my opinion shooting the 5.56 round in the heavy Galil select fire rifles when I was in the armed forces.

6mm rifles have very little recoil even in the lightest sporter models models at around 5-6lbs with standard loads in an average sporter rifle.


Rifle Recoil Table

Which IDF Unit did you serve in? I spent most of three years there in the eighties.

 

[lightwind]

WildRose: Have you ever looked at a real pressure curve for a rifle? If you had, you would see that the pressure maximizes long before the bullet leaves the rifle. For example please look at the following explanation:

Powders and cartridge testing

Where Roberto states:

"Subsequently the pressure curve during a cartridge test, as recorded in a pressure gun fitted with the same recording equipment as the closed bomb, is no longer ever rising. It first reaches a peak, then it suddenly decreases as the bullet continues down the barrel, falling to zero when the bullet leaves the muzzle."

The reason is that you want to get the most work out off the powder that you can. As the powder burns it builds pressure, however, the bullet moves and the volume becomes larger and the temperature starts dropping from a peak so the curve has its maximum before the bullet leaves the barrel.

I am absolutely sure you can out shoot me. However, you have not done a very good job of understanding any of the physics laid out here by me and some others. This is an opportunity for all of us to learn if you would take a shot at understanding the physics and helping us understand the shooting ramifications. We know to use a powder with characteristics that give us maximum work - but that is very difficult to come up with (hence all of the reloading experiments). The original question for this thread had to do with recoil and accuracy. The answer is extremely complicated and is the reason that people try many ways to reduce the motion of the rifle from the moment the trigger is pulled until the bullet has cleared the barrel. The field for this is called "internal ballistics." The physics we are using is not something we made up. It is the basic physics taught in a first physics class that covers statics and dynamics. Please try to understand what we are putting forward - unplant your feet - and look at the technical links that have been provided.

We have seen there are two sources of recoil.

1) The internal physics that take place from the time the trigger breaks until the time the bullet leaves the barrel. This has to do with a number of variables and is a subject in itself. It is the part of the recoil that you do not seem to believe in spite of all of the references that have been provided.

2) The external physics as the pressurized gas is released at high-speed from the end of the barrel. That rocket action is all that you seem to be able to believe.

The bottom line is that all of these issues have to do with rifle motion but the internal physics is what determines where the bullet will hit. The external physics is what gives additional recoil and does not have much of an effect on the projectile trajectory (since the bullet has left the house).

The initial component of internal motion recoil, vibration, and trigger action can affect the placement of the shot.

However, the addition of the second type of recoil can produce exaggerated flinch and trigger jerk that will also have influence on where the rifle moves before the bullet moves out of the barrel by influencing the internal ballistics.

You are right about muzzle brakes being very helpful (particularly for hot loads with a high ratio of powder mass to projectile mass) in reducing flinch. However, by ignoring the first type of recoil and other motions you are ignoring the forces that have an influence on bullet placement.

My bet is that you minimize these internal forces anyway when you shoot because of the way you were taught and the way you have learned. You just do not understand why. However, the question was not from you so I hope the initial poster has gotten something out of this free-for-all. I know I have. I have leaned from the sites I have visited to research the question as well as from the posts on the site. My thanks to all who have participated (yes, particularly you WildRose because you have made me dig for answers).

 

[WildRose]

Good article evaluating muzzle brakes with good solid experimental data.

Two of them reduced measured recoil by 63%. All but one reduced felt rearward recoil movement by over 50%.

http://www.multigunmedia.com/pk-compensation.pdf

 

[WildRose]

WildRose: Have you ever looked at a real pressure curve for a rifle? If you had, you would see that the pressure maximizes long before the bullet leaves the rifle. For example please look at the following explanation:

Powders and cartridge testing

Where Roberto states:

"Subsequently the pressure curve during a cartridge test, as recorded in a pressure gun fitted with the same recording equipment as the closed bomb, is no longer ever rising. It first reaches a peak, then it suddenly decreases as the bullet continues down the barrel, falling to zero when the bullet leaves the muzzle."

The reason is that you want to get the most work out off the powder that you can. As the powder burns it builds pressure, however, the bullet moves and the volume becomes larger and the temperature starts dropping from a peak so the curve has its maximum before the bullet leaves the barrel.

I am absolutely sure you can out shoot me. However, you have not done a very good job of understanding any of the physics laid out here by me and some others. This is an opportunity for all of us to learn if you would take a shot at understanding the physics and helping us understand the shooting ramifications. We know to use a powder with characteristics that give us maximum work - but that is very difficult to come up with (hence all of the reloading experiments). The original question for this thread had to do with recoil and accuracy. The answer is extremely complicated and is the reason that people try many ways to reduce the motion of the rifle from the moment the trigger is pulled until the bullet has cleared the barrel. The field for this is called "internal ballistics." The physics we are using is not something we made up. It is the basic physics taught in a first physics class that covers statics and dynamics. Please try to understand what we are putting forward - unplant your feet - and look at the technical links that have been provided.

We have seen there are two sources of recoil.

1) The internal physics that take place from the time the trigger breaks until the time the bullet leaves the barrel. This has to do with a number of variables and is a subject in itself. It is the part of the recoil that you do not seem to believe in spite of all of the references that have been provided.

2) The external physics as the pressurized gas is released at high-speed from the end of the barrel. That rocket action is all that you seem to be able to believe.

The bottom line is that all of these issues have to do with rifle motion but the internal physics is what determines where the bullet will hit. The external physics is what gives additional recoil and does not have much of an effect on the projectile trajectory (since the bullet has left the house).

The initial component of internal motion recoil, vibration, and trigger action can affect the placement of the shot.

However, the addition of the second type of recoil can produce exaggerated flinch and trigger jerk that will also have influence on where the rifle moves before the bullet moves out of the barrel by influencing the internal ballistics.

You are right about muzzle brakes being very helpful (particularly for hot loads with a high ratio of powder mass to projectile mass) in reducing flinch. However, by ignoring the first type of recoil and other motions you are ignoring the forces that have an influence on bullet placement.

My bet is that you minimize these internal forces anyway when you shoot because of the way you were taught and the way you have learned. You just do not understand why. However, the question was not from you so I hope the initial poster has gotten something out of this free-for-all. I know I have. I have leaned from the sites I have visited to research the question as well as from the posts on the site. My thanks to all who have participated (yes, particularly you WildRose because you have made me dig for answers).

Either I'm not writing/explaining well or you didnt' read his artcle too closely.

He supports my conention that as long as you have combustion continuing you have pressure building and increasing velocity.

Yes the pressure itself peaks when the bullet separates from the case, but the powder is not fully consumed at that point and the continued combustion continues to build pressure as the round continues down the barrel falling to zero when the bullet exits ie, the cork pops. If all the powder were consumed at the point of maximum pressure in the chamber, maximum velocity would be reached there and continue to drop as the round travels down the bbl. That is not the case.

Final report.
Usually there is no link between tests run in a closed bomb and in a pressure gun, unless it is possible to know when the combustion is completed. After some years of studies I have found the way to get this link. I can process a file recorded from a pressure gun test, identify the combustion end point and calculate specific impulse, specific energy and energy potential of the powder loaded into the cartridge tested.

The energy potential can be calculated because there is a body (the bullet) in motion, and some work is made on it. Obviously, the same is not possible in closed bomb tests, where nothing can move.

Should the combustion end beyond the muzzle, such figures can only be estimated on the basis of recorded trend.

The software can predict whether combustion ends within the muzzle. In addition, the burnt mass fraction and the form function of the powder can be plotted, the one vs. the relative specific impulse, the other vs. the burnt mass fraction.

The relative specific impulse is somewhat similar to the burnt width fraction, but it is more convenient as it can be referred to the whole mass of the load, instead of the mean minor dimension of kernels.

The form function is similar to the dynamic vivacity, but it is dimensionless. Nevertheless, the dynamic vivacity can be derived dividing the form function by the specific impulse.

I hope that my studies are of interest to some Guns and Shooting Online readers. (Even better if they intererst some cartridge factory to which I could sell my software!)

This is why we use the fastest buring powders in things like handguns, and the slowest burning powders in our large magum rifles.

In order to achieve maximum efficiency from the powder, we use the powders that will continue to burn for the full length of the barrel, with as little as possible waisted at the end.

If we used the fastest burning powders in our large magnums, in order to achieve equal velocities with the same bullets, the initial pressures would have to be so high that we'd either blow up the gun or at a minumum the throat erosion would be so dramatic a barrel would last only for a few rounds.

 

[lightwind]

WildRose: Let me try to get more specifics from you. It is my understanding from your writing (written exchanges can, sometimes be misinterpreted and I would like to be sure what you are saying). Please let me know if the following represents your positions:

1) You believe that there is no equal and opposite momentum increase in the rifle until the projectile leaves the barrel.

2) You believe that the rifle/projectile system is closed as opposed to open and that is the reason there is no net force imparted on the gun until the projectile leaves the barrel and that is transmitted by the rocket propulsion mechanism of the gases and projectile leaving the barrel. Everything up to that point does not contribute to recoil.

3) You believe that the pressure in the chamber increases until the projectile leaves the barrel.

4) You believe that we choose slower powders for longer barrels to be sure that the powder is burning all the way down the barrel which you believe is the reason the pressure increases to the end of the barrel.

Those are four of my interpretation of your statements that I can't agree with and I want to be sure that this is what you are really saying. You can assume that I disagree with those statements (with qualifications in details of the rocket type propulsion which I agree is significant but not the only source of recoil). Please correct me if I am wrong on these statements being a part of your understanding. I would not like to waste time arguing on a point we actually agree on.

 

[WildRose]

WildRose: Let me try to get more specifics from you. It is my understanding from your writing (written exchanges can, sometimes be misinterpreted and I would like to be sure what you are saying). Please let me know if the following represents your positions:

1) You believe that there is no equal and opposite momentum increase in the rifle until the projectile leaves the barrel.

No as I have stated I've done the math and a huge amount of shooting with various loads, same rifles comped/not and don't find it rises to the level of affecting accuracy to any significant degree. By far I find that the peak of recoil comes from the muzzle blast and the rocket motor effect. I find that at this point it is impossible to affect accuracy other than the shooters anticipation/reaction to said recoil.

Read the article I posted and look at his recoil sled experiments.

2) You believe that the rifle/projectile system is closed as opposed to open and that is the reason there is no net force imparted on the gun until the projectile leaves the barrel and that is transmitted by the rocket propulsion mechanism of the gases and projectile leaving the barrel. Everything up to that point does not contribute to recoil.

No, I believe correctly that what happens with inertia within the closed pressure vessel does not affect accuracy to any significant degree.

3) You believe that the pressure in the chamber increases until the projectile leaves the barrel.

No, as I stated, there is an initial peak, but as long as combustion continues pressure is created, thus driving the bullet to greater velocities with longer barrels and slower burning powders with less/equal chamber pressures as compared to faster burning powders.

4) You believe that we choose slower powders for longer barrels to be sure that the powder is burning all the way down the barrel which you believe is the reason the pressure increases to the end of the barrel.

No, that's not in any way what I stated. I never even suggested pressure is greatest at the end of the barrel. Pressure continues to be created as long as there is combustion within the closed pressure vessel. That pressure lessons as the total volume of area increases, but as long as combustion is occurring in the closed pressure vessel velocity is increasing because of said expansion due to combustion. Again, this is why we can achieve higher velocities with higher mass of the projectile with lower or equal chamber pressure vs faster burning, lower mass, shorter barrel.

If I were not correct on this point we would not use slower burning powders for our heavier projectiles and longer barrels. We would use the same fast burning powders for every load regardless of barrel length or mass of the projectile.

Those are four of my interpretation of your statements that I can't agree with and I want to be sure that this is what you are really saying. You can assume that I disagree with those statements (with qualifications in details of the rocket type propulsion which I agree is significant but not the only source of recoil). Please correct me if I am wrong on these statements being a part of your understanding. I would not like to waste time arguing on a point we actually agree on.

Which is perhaps I think the major source of our disagreement; my ability/lack there of to relate the info in such a manner as to get it across properly.

 

[lightwind]

WildRose: Please excuse my nit-picking but I am still not completely understanding a couple of your answers. Some of them are very close to my view and I am ready to agree to some of those. However, there are still some issues you brought up I don't fully understand.

A) You said (on page 13): "Incorrect, pressure continues to build as long as it is constrained by the bullett and it is still burning."

What I interpret "pressure continues to build" to mean is a monotonically increasing curve of pressure. Your qualification of the sentence was: "as long as it is constrained by the bullett and it is still burning." I take that to mean if you have a long burning powder that can still have particles burning as they leave the barrel the pressure would increase until the projectile leaves the barrel. That is very different from another statement of Roberto:

"Subsequently the pressure curve during a cartridge test, as recorded in a pressure gun fitted with the same recording equipment as the closed bomb, is no longer ever rising. It first reaches a peak, then it suddenly decreases as the bullet continues down the barrel, falling to zero when the bullet leaves the muzzle."

What Roberto is saying is that there is a peak pressure in the barrel before the projectile has exited. My understanding of Roberto's information was that we see a peak in a barrel even if the powder is burning when it leaves. There are two reasons for the decrease in pressure as the bullet travels down the bore. The first is that the volume into which the gas is expanding is increasing as the bullet moves down the bore. The second is that the temperature (even of combusting material) is being reduced by the expansion into the larger volume (these are subtle differences in that one involves they are both related to the thermodynamics equation of PV=NRT. Where P is pressure, V is volume, N is the number of units (such as moles), R is the molar gas content for the gas mixture, and T is the temperature. In this case we are looking at the effect on pressure as both T and V change. You challenge that by saying:

"He supports my contention that as long as you have combustion continuing you have pressure building and increasing velocity.

Yes the pressure itself peaks when the bullet separates from the case, but the powder is not fully consumed at that point and the continued combustion continues to build pressure as the round continues down the barrel falling to zero when the bullet exits ie, the cork pops. If all the powder were consumed at the point of maximum pressure in the chamber, maximum velocity would be reached there and continue to drop as the round travels down the bbl. That is not the case."

This statement is quite confusing. If pressure is continuing to build as long as you have combustion of the powder, that would mean it was increasing (building). However, in the next sentence you say: "Yes the pressure itself peaks when the bullet separates from the case." It can't be both. Either it peaks at the case or it peaks at the point where combustion stops. Which is is? Do you see why this confuses me?

Let me address the point about powder needing to be burning for the bullet to be accelerating: " If all the powder were consumed at the point of maximum pressure in the chamber, maximum velocity would be reached there and continue to drop as the round travels down the bbl." Let me explain why that is wrong. At every point in the barrel the pressure behind the bullet is greater than atmospheric pressure. The forces holding the bullet back in its acceleration are friction and atmospheric pressure. As long as the pressure from the rear of the bullet is larger than the pressure in front of the bullet by enough to to overcome friction the bullet will continue to accelerate (although at a lower rate). Consequently, as long as the pressure behind the bullet is substantially greater (and decreasing from the peak behind it) than the pressure in front the bullet will go faster, not slow down just because it is in front of the pressure peak regardless of powder burning or not. Do you see this point - or do we still disagree on this one?

I am going to hit the sack but I am enjoying the conversation. Your positions have forced me to do something I have wanted to do for a while and that is to apply science to shooting. I even picked up a good ballistics book that it looks like will take me a year to get through. I am sure you will have some of your own points and I look forward to them.