The force required to push a bullet into rifling...

guntech

guntech

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I am conducting a little test on the force required to seat a jacketed bullet from sitting in the throat to be pushed 3/4's of an inch into the rifling.

I am using a piece of new barrel and a 300 grain .338 bullet.

338-300-grain.jpg


This test was following what I had to do to remove a bullet that was driven by a primer only - fully into the rifling on a .300 Savage. Extremely hard to drive out with a flat ended steel rod.

In this test the bullet pushed into the rifling about half way and then the back of the bullet started to deform... at 180 pounds on the press.
It took 150 pounds to push the bullet out.

I can only speculate the primer drove the bullet as far as it did because of the pressure and the momentum behind the moving bullet...
 
ive done experiments with dud rounds after a friend had one.
30-06 with 150 gr bullet cci large rifle primer only. bullet didint move.
223 55 gr bullet cci 450 primer, bullet didnt move.
17 hornet with 20 gr bullet and a cci 450 primer, bullet was stuck in the lands, and came out with one or 2 taps on an old cleaning rod.
 
It would be very interesting to find out how much is the minimum amount of gun powder to drive the bullet right through the barrel.
 
Dennis,
Make up another piece with a long freebore to support the bullet and a shaped punch to apply the force. I would also like for you to test bullets coated with moly; with and without carnuba wax. Maybe shove a couple of Barnes bullets through as well. Do all of this for free, of course, and post your findings. I could do this myself but it's easier to see you do it. ;)
By the way, I omitted the powder from a cartridge for my 303 when I was 15. The bullet, a 125 Sierra, 30 cal, was started into the rifling but not very far. This was lucky for me because, not realizing what had happened, I simply ejected that one and attempted to chamber another but the bullet which was stuck in the throat prevent me from doing so. If I had been able to chamber the next round, I would have shot it with likely catastrophic results. Young and stupid. The bullet came out fairly easily. Regards, Bill
 
guntech said:
I am conducting a little test on the force required to seat a jacketed bullet from sitting in the throat to be pushed 3/4's of an inch into the rifling.

I am using a piece of new barrel and a 300 grain .338 bullet.
...

In this test the bullet pushed into the rifling about half way and then the back of the bullet started to deform... at 180 pounds on the press.
It took 150 pounds to push the bullet out.
Click to expand...

Thanks for that report! Tells me that a jacketed bullet, at the rear end, will deform until it hits support, when trying to overcome resistance of entering the bore / engraving the rifling - so, suggests that bullet rear end actually deform to fill the throat area, rather than "rattle on through". Without having one on hand to measure, if we assume the flat end of that Sierra bullet was 0.30" diameter, what your press was pushing on, then that is .0707 square inches. 180 pounds of force applied, so that rear end was seeing about 2,546 PSI - I think? So, a long way from the 60,000 to 65,000 PSI that many 338 belted cartridges would apply to that bullet?? But very conceivable that just a primer might get PSI to that level?

And, as you mentioned, that still required 150 pounds force to push it back out of there!
 
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Am I correct in understanding that the base is supposed to expand under combustion pressure to obturate even with jacketed bullets?

Not like the solid copper ones that come with cute little sealing rings turned into which are just engraved down.
 
I have a brass rod that measures .2805 diameter and 9.25" long.
Two drops to dislodge a 30 Cal bullet in the lands.
Don't know where I came up with this rod but have researched getting other rods of different diameters without success.
Have a braising rod from a welding supply shop to push fired rimfire brass out but don't know if it would damage the crown.
This rod appears to have a copper looking coating. Checked it with a magnet and it is ferrous.
Might see if a wrap of electrical tape will still allow it to enter the bore . . . much like Dennis protected his bullet pushing steel rod.
 
Rayleigh_Scattering said:
Am I correct in understanding that the base is supposed to expand under combustion pressure to obturate even with jacketed bullets?

Not like the solid copper ones that come with cute little sealing rings turned into which are just engraved down.
Click to expand...

I do not know what a jacketed bullet base is "supposed" to do, but Guntech's experiment is first that I have read - seems to say that straight pressure on rear base of jacketed bullet will cause that bullet to distort - I presume meaning it gets "fatter" - as the friction of the rifle bore and the rifling engraving is being overcome. I have never used solid copper bullets, so I have no experience about a "sealing ring" on them. Would not be the first shooting gizmo invented by and for the marketing people - but I do not know... In rifles that I have, not unusual to have a "ball seat" or throat just ahead of chamber neck cut, that is a bit larger than is the groove diameter in the barrel. So, a "fatter" bullet can rest within the throat, but gets swaged down as it passes into the rifled bore, besides having the rifling engraved. It was an apparently "long ago" principle with lead cast bullets to size them to fit snugly in the throat, which is often a smidgeon larger diameter than the groove diameter...
 
horseman2 said:
I have a brass rod that measures .2805 diameter and 9.25" long.
Two drops to dislodge a 30 Cal bullet in the lands.
Don't know where I came up with this rod but have researched getting other rods of different diameters without success.
Have a braising rod from a welding supply shop to push fired rimfire brass out but don't know if it would damage the crown.
This rod appears to have a copper looking coating. Checked it with a magnet and it is ferrous.
Might see if a wrap of electrical tape will still allow it to enter the bore . . . much like Dennis protected his bullet pushing steel rod.
Click to expand...

That may knock a bullet out that has just engaged the rifling ever so slightly... but it will never move a bullet that is fully into rifling.
 
There was a study that used a pretty similar methodology done on 308 projectiles back in the early 2000s. I stumbled across it when I was puzzling over shot start pressures in QL.

So to answer Mr. Leeper's request for moly, no moly, and Barnes, I submit the following :d

EngravingForce.jpg

Source and methodology is here:
https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2004/arms/session9/siewert.ppt
 

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Good on you for that post, Harwood! Being "old guy", the "Push Force" scale, in Newtons, didn't mean much - had to look it up - the 180 pounds force that Guntech was applying is something like 800 Newtons. He got the results that he got with .338"; looks like "NDIA Small Arms" got the results that they got with .308". Can pretty much go "cross eyed" in that .ppt link that you gave, for further detail about that testing!!! No doubt, though, it seems, that the solid copper bullets - Barnes were used I think it said - pretty much need more force than others...
 
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What has been done is a comparison of different bullets pushed into a bore and the force required to do that.

There are at least 3 components of pressure to get a velocity.

That is Start Pressure, Pressure to drive bullet to exit and Muzzle pressure.

One load in my 7mm-08 has a start pressure of 10 445 psi + pressure required to reach muzzle 39 255 psi and muzzle pressure 10 232 psi for a total pressure of 59 932 psi. This is in a 20" bbl, if the barrel was longer the muzzle pressure will be less, start pressure the same, and more available pressure to push the bullet down the bore, therefore velocity will be higher.

The jump is ~0.013", this means the bullet travels 13 thou then slams into the rifling in about 0.02 mS, then travels another inch or so to reach max chamber pressure, 0.2 mS. There is decreasing pressure to the muzzle were it is exhausted. The exhaust provides no real useful work, just a little rocket effect as the bullet clears the muzzle.

So, the experiment described does have merit in selecting bullet construction, size and type of gilding metal, as , for example a mono-bullet does not obturate to the extent of a lead core jacketed bullet, there fore more force is required.

While nice to know, these numbers have no correlation to what happens in the chamber during the firing event.

As the pressure/velocity increases so does the resistance due to the time component.
 
Sounds good, BCBRAD - I suspect that your pressure numbers come from some software?? Not certain I know of any real world pressure measuring devices that can do psi pressure, within a barrel, to 5 significant digits, but maybe such a thing exists. Reviewing what you wrote - if your pressure numbers are produced by software, and not actual measurements, how do you know you meet your criteria in your second last line - "what happens in the chamber during the firing event"?? Just an old guy wondering...
 
The base of the bullet probably doesnt bump up very big or to fill the throat area of the chamber during firing like it did while being pushed like in this case.

Lead bullets are made with a cavity in the back to allow them to pump up. Im sure with a jacketed bullet there may be some distortion but not very much. The bullet wouldnt be just pushed by the back. The pressure would be all around it as well. Meaning there is equal pressure on the sides keeping its shape as there is pressure pushing the base of the bullet.

Same goes for really long cast bullets loaded deep into the case below the shoulder. It keep its shape in the case as the pressure is from all sides and back evenly.
 
Potashminer said:
Sounds good, BCBRAD - I suspect that your pressure numbers come from some software?? Not certain I know of any real world pressure measuring devices that can do psi pressure, within a barrel, to 5 significant digits, but maybe such a thing exists. Reviewing what you wrote - if your pressure numbers are produced by software, and not actual measurements, how do you know you meet your criteria in your second last line - "what happens in the chamber during the firing event"?? Just an old guy wondering...
Click to expand...

This information is gleaned from software.

As an example , the pressure trace system also requires soft ware to produce a result. https://www.shootingsoftware.com/pressure.htm

I can not comment on the afore mentioned system as i have not used it.

I have studied QuickLoad over the last several years, and still studying.

With this soft ware velocity is the criteria which all calculations hinge upon, as are accurate inputs of weights and measures.
QuickLoad (QL) does the math for the user.

I have no way of knowing if the pressure numbers are accurate, but what I do know is that they are close, as the math works.

I have back engineered many good loads formulated by traditional means, also have taken 'most accurate powder and charges' from reloading manuals, Nosler is a good one for doing that.

QL can get you an excellent hunting load within 10 shots, for competition I like to shoot a lot of rounds to see if it will stand up in different conditions and tweak the ES down to as low as I can get it.

What happens during the firing event:

Basically in the ~the first 0.02mS the powder starts to combust, small spike in pressure, the bullet moves to the rifling 2nd larger spike in pressure ~0.2 mS and between an inch and 1.5 inches there abouts down the bore, if you use an incompatible powder then the powder charge could go 'plastic' and there could be a 3rd spike in pressure that is more like an explosion, can ring the barrel or blow it up. The total event takes 0.8 to 1.5 mS depending on acceleration rate, velocity and barrel length until the bullet exits along with the gas stream at high pressure. That is how I interpret it and it is a basic understanding.

QL provides the user with a lot of information , not always plain to see but it is there.

Just an old guy trying to explain.
 
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