recoil v accuracy

[WildRose]

But we keep the pressure the same or close as we can and we use less powder with the heavier bullet, which translates into less propellent at the end of the muzzle but if we go from a 225gr bullet to a 300gr bullet the recoil difference is significantly increased with a lighter charge of powder at the same pressures.

That wasn't what I was addressing.

However the same principle applies. In a closed pressure vessel where the object is to eject a projectile, the greater the mass of the projectile the greater the pressure generated by the smaller amount of propellant. Greater resistance, greater pressure, greater heat with the larger/heavier bullet is the net result, or an equal amount of same with the heavier bullet/smaller powder charge vs the lighter bullet/heavier powder charge.

More force driving the heavier mass means a greater ejecta or rocket effect acting against the rifle when it is all ejected.

 

[lightwind]

WildRose: You still haven't got it right. It is not a closed system (as most of those replying have pointed out). Considering the barrel with the bullet moving through to be a closed system it is causing you to misinterpret the physics. The powder is doing work on the bullet. The result is force which translates to acceleration which is the same in both directions to keep a zero momentum for the system (near zero because of irreversibility in the system). The fast hot gases at the end are an important part of the recoil, but as has been pointed out multiple times before, it is only one of the two important parts of recoil.

 

[westcliffe01]

Wildrose, the best analogy I can make is an astronaut in outer space throwing a spear. If you push the spear away from you, you are going to end up going in the opposite direction to the spear. Your speed vs the spears speed is the inverse of the ratio of your mass vs the spears mass. Note that there is no propellant or muzzle blast involved. Action = reaction.

The same would be true if you were pushing a bullet out of a tube by hand. Since our hands are not too fast, imagine trying to push a cannon ball out a cannon barrel. Even if the ball slides in the barrel on an air bearing (no friction), if you accelerate the ball, it is going to be pushing back on your hand. Try that in outer space with no land under your feet and no gravity to hold you down and create friction to keep you stationary and you will be moving back away from the breech while the ball is moving out the breech.

Arguing that all recoil is due only to muzzle blast is wrong and has no basis in math or science. The fact that muzzle blast may be more perceptible than the impulse from the bullet is a completely subjective observation and does not detract from the truth. Since muzzle blast starts only after the bullet has left the barrel, it is highly unlikely to influence point of impact (except for causing the shooter to flinch when he pulls the trigger next time). The impulse of the bullet, however, takes place while the bullet is moving in the barrel.

Considering that a 1" shift in point of impact at 100yds requires only a deflection of 0.006" at the end of a 22" barrel, it seems entirely possible that movement of the weapon due to the way it is held and the force exerted by the impulse of the bullet could contribute towards a degradation in accuracy.

This last paragraph is nothing new, it is what marksmanship instructors drill into you day and night. Assume the "correct" position, develop the right grip, look to see what the muzzle does if you close your eyes, etc etc. But bigger heavier bullets will have a larger impulse, will accelerate more slowly and very likely will travel down a longer barrel, providing more opportunity for point of impact to shift compared to a 32gr Vmax going 4000fps.

 

[Boss Hoss]

I was getting a good chuckle out of this thread and sent an email to my Smith who sent this back to me. He is also a BR HOF member.



"JUST STD PHYSICS. NEWTON'S LAWS "EVERY ACTION HAS AN EQUAL AND OPPOSITE REACTION" & "A BODY AT REST, REMAINS AT REST UNTIL ACTED UPON BY AN EXTERNAL FORCE". F= Ma."

 

[WildRose]

Wildrose, the best analogy I can make is an astronaut in outer space throwing a spear. If you push the spear away from you, you are going to end up going in the opposite direction to the spear. Your speed vs the spears speed is the inverse of the ratio of your mass vs the spears mass. Note that there is no propellant or muzzle blast involved. Action = reaction.

The same would be true if you were pushing a bullet out of a tube by hand. Since our hands are not too fast, imagine trying to push a cannon ball out a cannon barrel. Even if the ball slides in the barrel on an air bearing (no friction), if you accelerate the ball, it is going to be pushing back on your hand. Try that in outer space with no land under your feet and no gravity to hold you down and create friction to keep you stationary and you will be moving back away from the breech while the ball is moving out the breech.

Arguing that all recoil is due only to muzzle blast is wrong and has no basis in math or science. The fact that muzzle blast may be more perceptible than the impulse from the bullet is a completely subjective observation and does not detract from the truth. Since muzzle blast starts only after the bullet has left the barrel, it is highly unlikely to influence point of impact (except for causing the shooter to flinch when he pulls the trigger next time). The impulse of the bullet, however, takes place while the bullet is moving in the barrel.

Considering that a 1" shift in point of impact at 100yds requires only a deflection of 0.006" at the end of a 22" barrel, it seems entirely possible that movement of the weapon due to the way it is held and the force exerted by the impulse of the bullet could contribute towards a degradation in accuracy.

This last paragraph is nothing new, it is what marksmanship instructors drill into you day and night. Assume the "correct" position, develop the right grip, look to see what the muzzle does if you close your eyes, etc etc. But bigger heavier bullets will have a larger impulse, will accelerate more slowly and very likely will travel down a longer barrel, providing more opportunity for point of impact to shift compared to a 32gr Vmax going 4000fps.

An astronaut in space is not acting within a sealed pressure vessel. The explosion in the chamber of a rifle is.

 

[WildRose]

WildRose: You still haven't got it right. It is not a closed system (as most of those replying have pointed out). Considering the barrel with the bullet moving through to be a closed system it is causing you to misinterpret the physics. The powder is doing work on the bullet. The result is force which translates to acceleration which is the same in both directions to keep a zero momentum for the system (near zero because of irreversibility in the system). The fast hot gases at the end are an important part of the recoil, but as has been pointed out multiple times before, it is only one of the two important parts of recoil.

And again, an explosion in a sealed pressure vessel is what we are talking about here.

I've run the numbers, I've shown the videos. The amount of intertial forces at work are not enough to generate a significant force to affect accuracy.

The primary driver or recoil is the expulsion of hot gasses and the projectile at the end of the bbl.

At that point in time, not before you have an definable, measurable outside force pushing the rifle backwards from the jet of hot gasses/rocket action.

Mass of the Rifle vs Mass of the bullet.

8lbs rifle=8x7000gr=54,000gr

One Bullett=200gr=Mass being driven.

Mass of rifle is 270x greater than that of the projectile.

 

[westcliffe01]

You would be right, but only if the bullet didn't move. That open muzzle betrays the fact that it is not a "sealed pressure vessel". The bullet is like a rail car on a railway line. That is not a "sealed pressure vessel" either.

An astronaut in space is not acting within a sealed pressure vessel. The explosion in the chamber of a rifle is.

 

[lightwind]

Exactly right Boss: Said: ""JUST STD PHYSICS. NEWTON'S LAWS "EVERY ACTION HAS AN EQUAL AND OPPOSITE REACTION" & "A BODY AT REST, REMAINS AT REST UNTIL ACTED UPON BY AN EXTERNAL FORCE". F= Ma."

That sounds close to my prior posts:

" The equal and opposite force is against the bolt face."

"The bottom line is conservation of momentum"

"Newton showed that "an object in motion stays in motion" ... "That includes a situation where the object is at rest with respect to the observer applying the force." Which is the same as "A BODY AT REST, REMAINS AT REST UNTIL ACTED UPON BY AN EXTERNAL FORCE" for an observer in the same inertial frame of the body.

I completely agree with your friend's view.

"any amount of force will cause it to accelerate in accordance with F = m*a."

 

[WildRose]

I was getting a good chuckle out of this thread and sent an email to my Smith who sent this back to me. He is also a BR HOF member.



"JUST STD PHYSICS. NEWTON'S LAWS "EVERY ACTION HAS AN EQUAL AND OPPOSITE REACTION" & "A BODY AT REST, REMAINS AT REST UNTIL ACTED UPON BY AN EXTERNAL FORCE". F= Ma."

Emphasis mine.

The only external force here is the barometric pressure/air density resistance in the barrel ahead of the bullet.

All other forces at work are contained within the pressure vessel until such time as the bullet exits, other than the miniscule amount of gas that escapes around the bullet as it travels through the barrel.

 

[WildRose]

You would be right, but only if the bullet didn't move. That open muzzle betrays the fact that it is not a "sealed pressure vessel". The bullet is like a rail car on a railway line. That is not a "sealed pressure vessel" either.

It is a sealed pressure vessel until it is vented.

This is what happens when it's not properly vented.



Would you like to explain to me again how this is not a pressure vessel we are talking about?

 

[westcliffe01]

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.

Emphasis mine.

The only external force here is the barometric pressure/air density resistance in the barrel ahead of the bullet.

All other forces at work are contained within the pressure vessel until such time as the bullet exits, other than the miniscule amount of gas that escapes around the bullet as it travels through the barrel.

 

[lightwind]

WildRose: The video you put up IS a pressure vessel (closed system) with walls that failed. A normal gun is not. The bullet moves down the barrel and keeps the pressure from exceeding maximum pressure and is an open system (the moving projectile open to the atmosphere). If you continue to think that a normal gun with a normal bullet is a closed system you will never realize how momentum is transferred.

 

[westcliffe01]

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.

 

[WildRose]

WildRose: The video you put up IS a pressure vessel (closed system) with walls that failed. A normal gun is not. The bullet moves down the barrel and keeps the pressure from exceeding maximum pressure and is an open system (the moving projectile open to the atmosphere). If you continue to think that a normal gun with a normal bullet is a closed system you will never realize how momentum is transferred.

No it is a closed pressure vessel that is vented in one place.

Until the bullet exits the pressure is contained between it, and the bolt face.

The nominal pressure exerted against the bullet from the exterior forces of the density of the air ahead of it, are the only external forces acting against said bullet.

The gun blew up, because the vet was stopped up due to obstruction.

In order for the forces to be equal against both the bullet and the rife, would be for the bullet's mass plus friction to equal the mass of the rifle.

Work the formulas you guys keep repeating using the values I did and get back with me.