How Much Force A Bullet Exerts Against The Rifling

[vzerone]

More correctly how much force a bullet exerts against the sides (or walls) of the lands. I have a formula for that, but their are a lot of variables. One is the number of rifling grooves. Another is where you calculate for the pressure meaning this formula is for peak pressure (or when the bullet is moving at it's highest velocity in the barrel). The example in the formula is a .25 caliber bullet with a velocity of 2500 fps fired in a 1 and 12 rifling with 6 grooves. The answer is 4900 pounds. We know that a faster twist would raise that number. Now do those of you still feel that the torque applied to a cast bullet is enough that it is indeed the faster rifling twists that is damaging the bullet in some manner that it becomes inaccurate? Here's the formula:

[DougGuy]

No one that I know can read that 29kb file and if you blow it up to a readable size you still can't read it. I don't agree at all with your math. If a rifle had that much torque applied against the rifling, NO HUMAN could hold on to it and fire it.

[geargnasher]

Didn't I mention that to you in email like a year ago? Right there under our noses in TBF all this time. I did calcs when I found that for M1A 11-twist and bearing surface of engraved (but not bumped-up) 30 sil. bullet, came up with around 10K psi on sides of lands at 2200 fps, way under 50/50 alloy strength. Pretty much settled what we and DrB were talking about way back....bullet ain't gonna strip unless it's made from linotype or similar that will literally abrade away at hv. Gotta have the right alloy for pressure/velocity which means not hard/bittle/flaky and not too much tin....like SOMEONE has been telling us for years.

Gear

[vzerone]

No one that I know can read that 29kb file and if you blow it up to a readable size you still can't read it. I don't agree at all with your math. If a rifle had that much torque applied against the rifling, NO HUMAN could hold on to it and fire it.

Well that is your opinion, but I don't agree with it. The formula is correct. Take for example if the peak pressure pushing the bullet is 52,000 PSI what would you assume the force of the bullet against the rifling to be, some very low number? BTW the the physicist that figured these formulas up also were questioned as to what was the force in pounds that the bullet torques or twist the rifle in your hands and it's very very low. An example figure like .031.

I'll try to enlarge and repost that image.

[geargnasher]

No one that I know can read that 29kb file and if you blow it up to a readable size you still can't read it. I don't agree at all with your math. If a rifle had that much torque applied against the rifling, NO HUMAN could hold on to it and fire it.

If a rifle put nearly 3,000 lb/ft of energy into a bullet it would knock you over backwards 20 feet if you fired it......Except they DO and IT DOESN'T. I think you're not understanding about the A in F=MA, DougGuy, or the scale on which these forces are applied. You can actually feel the torque of a .308 rifle or even a handgun in your hand if you pay attention to it.

Download The bullet's Flight by F.W. Mann from Castpics and read the whole section that page is from, it gives a full explanation of how the formulas was derived with consideration to certain parts of the equation which make it not precisely accurate but so nearly so as to be inconsequential for our purposes.

Gear

[vzerone]

Didn't I mention that to you in email like a year ago? Right there under our noses in TBF all this time. I did calcs when I found that for M1A 11-twist and bearing surface of engraved (but not bumped-up) 30 sil. bullet, came up with around 10K psi on sides of lands at 2200 fps, way under 50/50 alloy strength. Pretty much settled what we and DrB were talking about way back....bullet ain't gonna strip unless it's made from linotype or similar that will literally abrade away at hv. Gotta have the right alloy for pressure/velocity which means not hard/bittle/flaky and not too much tin....like SOMEONE has been telling us for years.

Gear

Are you talking to talking to DougGuy as I don't know you??

[geargnasher]

Of course you know me. But no matter, this formula you posted settles a whole lot of questions about trailing edge failure and alloy failure. I didn't bring it up here when I found it because it contradicts popular opinion and everything Molly tried so hard to convince us of about velocity limits of cast bullets. This should be a great discussion if folks will read carefully and keep an open mind.

Gear

[DougGuy]

I hardly notice torque in my .308 and I use 180gr @ about 2400fps but I BIG TIME notice torque in a Vaquero with a Lee 300gr over a full house load of H110, as it turns the gun completely sideways in your hands regardless of how hard you fight against it. I just can't imagine the torque forces are in the thousands of ft lbs.

[geargnasher]

....but those ft/lbs torque are pulling on a "lever" only one bullet radius long...i.e. not much mechanical advantage.

Gear

[vzerone]

I redid the image, looks like the other one is there too. Oh well at least you can read it now.

[W.R.Buchanan]

Given the same velocity, the faster twist barrel will have more of a negative effect than the slower twist barrel,,, but only after the RPM Threshold for that "particular boolit" has been exceeded.

Below that point it's all about RPM's, and every Bullet/Boolit has a sweet spot for RPM's that it likes best. Once that speed has been exceeded it is probably is more about balance than actual damage to the Bullet/Boolit, and at this point accuracy could start to suffer.

Only under extreme circumstances would Boolit Damage due to excessive speed become a factor. In order to achieve such velocity the boolit would have to be pushed so hard that it would probably result in deformation of the base of the boolit. This is where the problems start, as we all know the rear end is the "steering end." Once again this is not due to rotational torque being applied, but base deformation due to high pressure.

At chamber pressures a bullet is essentially fluid as it is being shoved thru the bore. How fluid it is, depends on the pressure applied and the material the bullet is made from. They actually make steel bullets! I have the drawings for them in my shop! They go thru the barrel just fine as very little known to man can stop a 60,000psi kick in the butt. Even Water will go thru steel at 60,000 psi as witnessed by Water Jet Cutting Machines.

This is also why they invented Jacketed Bullets. They can absorb more pressure without deformation than lead boolits can. This results in Higher Velocities, Better Accuracy, Flatter Trajectories, and overall more useful Point Blank Range for a given Caliber/Cartridge/Weapons System... Still deformation of the base of a jacketed bullet has the same effect as it does on a lead boolit.

It upsets the rotational balance of the projectile as it travels down range.

I doubt that "rotational torque" would actually become a significant factor until the boolit actually stripped thru the rifling, and at that point the actual effect would be not enough rotation being transferred to the boolit, as opposed to too much rotation,,, thus resulting in instability.

I do not see being able to quantify this mathematically as being a useful tool. You can just work the bullet's speed up until the accuracy goes away, back off, and achieve an exact result as opposed to a theoretical result,,, which you still have to prove by practical application.

My .02

Randy

[vzerone]

Forget about the torque applied to the rifle from the bullet. I'm concerned with the force of the bullet against the rifling. I want to know if this force is high enough to damage the bullet that's it's accuracy deteriorates. Say that it does when you're pushing it very hard such as in high velocity. What exactly does it change? After all the bullet is confined in the bore.....what changes? I tried pushing pure lead bullets in various caliber trying on purpose to get the bullet to strip and I mean strip entirely. Unfortunately I only examined the bore after firing as I couldn't recover the bullet undamages (especially being pure lead). Say it did strip, wouldn't the grooves be filled with lead? There was no evidence of that. In fact I was surprised that the bore looked rather good. If someone could nail exactly what changing on the bullet then we can work on trying to alleviating that. Then I question myself that whatever happens to the bullet in the bore only show's up after exiting the bore.

[W.R.Buchanan]

If the boolit is plain based then when you drive it hard enough to strip the rifling you have also deformed the base. The combination of the two kills accuracy. But as you slow down to where you aren't stripping the rifling you still are deforming the base of the boolit because you are still above the threshold of Training Edge Failure.

As the base melts away blow by will occur, and thus barrel leading. In the case of stripped rifling the excess metal stripped off the boolit is blown out the end with the rest of the boolit,,, just not in one piece. Or since the groves are only .004-.005 deep on a side the boolit is probably just being swaged to bore size as opposed to having that material cut from the outside.

This is why you can't get any accuracy from a plain based boolit beyond 1500-1600 fps. The combination of Friction caused by Speed and Heat from the charge is deforming the base of the boolit. IE; Tailing Edge Failure.

Randy

[vzerone]

I don't believe in a cast bullet being fluid or even in the elastic/plastic state while in the bore. If it really was in a true fluid state the gas would blow it out of the barrel as an alloy spray of liquid. I also don't believe if it was in any of those states that when it leaves the barrel that it changes back to the state it was before you shot it and maintain the accuracy that it does. It only has microseconds upon ejection from the muzzle to change back and there are a lot of negative influences on it that would literally explode it near the muzzle and that's just not happening.

I don't believe in a sweet spot either. If a bullet is truly perfect the rotation of it doesn't affect it. There are too many motors and other apparatuses out there that have a spinning shaft that have mind boggling rpm. It's damn near impossible, for a bullet that is already spinning in the barrel, to make the transition from the barrel to the atmosphere with absolutely nothing changing. Most often the change that does happen is restabilized by the gyroscopic action of the bullet spinning. That action will fight hard to keep the bullet on it's path. I have fired bullets way beyond what they should have been going, and yes they key holed, but the interesting thing is they still printed a 2.5 to 3 inch group on the target....although not in the same area of the target that the same bullet printed it's group when it was stabilized.

[geargnasher]

Land pressure alone won't strip an engraved bullet...but abrasion from rubbing hard, brittle alloy across the leading edge of the rifling at HV with brittle alloy can erode enough to strip...plus once wear starts the gap, gas will blast by on the trailing edge and start chewing it away from the back side.

I think this is the whole reason that 10 twist .30 cals don't shoot good HV groups with Linotype but work great with 50/50 alloy and the exact right pressure curve.

Gear

[Ballistics in Scotland]

The area of the rear of a .257 bullet is 0.051875 of a square inch. Is there some way 50,000psi can exert a force of more than about 2500 pounds? Some of that is diverted into overcoming friction, but the greater part is devoted to driving the bullet forwards.ere

A point in danger of being dwarfed by the above very large one is that sliding friction varies in proportion to the force pressing two surfaces together, and with the coefficient of friction specific to that combination of materials. But in theory it doesn't vary at all with the area in contact. If a one-ton sledge is short, it will have more weight per square inch of runners, and thus the same one-ton force pressing on the ground.

This isn't perfectly true in practice. A short sledge will have its motion translated into more pitching and tossing as it encounters small inclines and obstructions in its way. But it will be very close to true with a normal bullet and smooth barrel surface. The number and depth of grooves makes very little difference. The rifling pitch will make some, however.

[W.R.Buchanan]

There are varying degrees of "Fluidity." Glass is a fluid. Believe me bullets no matter what they are made from are fluid when the pass thru a barrel. If they weren't they couldn't be engraved by the rifling. If the rifling was simply shearing the material off the bullet then there would be chips leftover. The excess metal is being swaged into a different form and the displaced metal is simply moved to a different position on the bullet.

Metal chips which result from being cut off a bigger piece are fluid when they separate from the piece being machined. Sometimes they stick to the cutting tool much like lead sticks to a barrel. Lubrication and cooling offset this effect, same as in a barrel.

A bullet traveling thru a barrel is undergoing a "Swaging Process." and a Swaging Process relies on Fluidity of the material in order to happen.

Next:

All entities have a "Resonance Frequency" and once that frequency is amplified past a certain level,,, that entity explodes.

However below that point, The ability of the entity to tolerate lesser forces are products of materials and design and speed of movement. Also those forces do influence the entity greatly, they just don't allow it to blow up.

In other words before destruction happens, the harmonic frequency ranges that are generated by the entities movement are being tolerated. But they can make it go stupid.

There is no such thing as 100% perfect balance. Perfection is unobtainable. Bullets are very close but they are not perfect. If they were perfect then rotational speed would not affect them. However it does affect them and the reason why is the vibration caused by the speed of rotation and the amount of "out of balance" present.

But the actual force involved here that is causing the bullet to deviate from it's intended path is "Centrifugal Force," and that force is acting on the out of balance factor of the rotating entity.

If there was no out of balance factor present IE: perfect balance,,, then the only thing Centrifugal Force could affect would be the "surface tension" of the material being spun. Once that was exceeded, the entity would explode.

As long as that speed of rotation was not exceeded, the entity would continue on it's intended path only being influenced by gravity.


The sweet spot referred to above includes the design of the bullet as well as material and can only be expressed as a range since it is impossible to exactly quantify all the factors of the materials composition that would affect the percentage of out of balance inherent within that one bullet or group of bullets/boolits. Thus a range is given which has proven to be successful to varying degrees.

There are no absolutes!

It effectively is an average of all those factors which nobody cares about, because that level of Minutia does not have enough of an influence on performance to alter the effectiveness of that bullet for it's intended purpose.

It is possible for an individual to make something work without completely understanding how or why it works. It would be nice to understand exactly all that contributes to the function of something, however there are so many things out there to figure out that a person might not actually get much done in a lifetime, or two.

Unfortunately there is no one answer to everything. People have been looking for it since the beginning of time, nobody's got close.

What I have found successful is a good basic understanding of what I'm doing which gives me the ability to accomplish my goal for that thing. That knowledge often translates to other disciplines and can have a logarithmic effect. IE: the more you know the better off you are.

See my signature below.

Randy

[Ballistics in Scotland]

Download The bullet's Flight by F.W. Mann from Castpics and read the whole section that page is from, it gives a full explanation of how the formulas was derived with consideration to certain parts of the equation which make it not precisely accurate but so nearly so as to be inconsequential for our purposes.

It also explains that a cast bullet is somewhat plastic under at least the first impact of maximum pressure, although of course nowhere near liquid. That is why a fairly soft alloy should upset to seal the bore, when a very hard one may not, and as a result will lead more. Only it shouldn't deform much. There may be some bluntening of the nose shape, and this is probably the reason why cast bullets often don't give good accuracy with the sort of sharp point which works with jacketed. Upsetting of the nose is likely to be assmmetrical, and although it isn't as important to accuracy as the base, it isn't negligible.

[vzerone]

Randy,

The point I was coming from is that many on this forum believe the bullet is near being in liquid state or more correctly that it is in a soft putty state. You're coming from the engineering aspects in which you are correct. Everything in the our world that rotates does have a limit or it explodes or becomes dangerous.

Those stripping test I performed where done with a large white paper sheet so many feet in front of the barrel and there was no lead holes that showed up on that paper other then the bullet hole. I just don't believe a rifle bullet will strip totally.

[vzerone]

The area of the rear of a .257 bullet is 0.051875 of a square inch. Is there some way 50,000psi can exert a force of more than about 2500 pounds? Some of that is diverted into overcoming friction, but the greater part is devoted to driving the bullet forwards.ere

A point in danger of being dwarfed by the above very large one is that sliding friction varies in proportion to the force pressing two surfaces together, and with the coefficient of friction specific to that combination of materials. But in theory it doesn't vary at all with the area in contact. If a one-ton sledge is short, it will have more weight per square inch of runners, and thus the same one-ton force pressing on the ground.

This isn't perfectly true in practice. A short sledge will have its motion translated into more pitching and tossing as it encounters small inclines and obstructions in its way. But it will be very close to true with a normal bullet and smooth barrel surface. The number and depth of grooves makes very little difference. The rifling pitch will make some, however.

BIS, it does too matter how many rifling grooves there are and their depth. I have a friend that manufacturers 6.8 Rem AR's. He has exceeded everyone else velocities by a whopping figure and safely. He does it by going to a slower twist, three groove rifling, and different groove depth.