Anyone ever measure the force required to push a bullet through a barrel? Really curious as the difference between heavy wall and thin wall jacketed bullets, as well as, the monolithic copper and bronze solids with and without driving bands.

Something else of interest would be if the force drops off any after the riflig has been engraved or if it stays relatively constant. If it does drop off, how much?

ASS_CLOWN

Surely somebody's done these measurements, but I've never seen any figures.

I have pushed lead slugs through bores to measure them. The force is much higher during the initial engraving than while pushing the engraved slug on down the bore. Takes a mallet to get it started, but in a smooth well oiled bore it can be pushed by hand after that.

Ackley did some experiments on this, and apparently the engraving force is not very large. He was shooting much oversized bullets through a bore, and there was surprisingly little increase in peak pressure.

I have a '69 264WM FN Musketeer new.While FN in their wisdom used a barrel with a lot of lands,the primer popped at <3050f/s with IMR7828,both powder weight and velocity under book max.I have had the rifle rebarreled after that.So I think your question has a lot of merit.

It's an interesting question certain enough. I use polygonal rifles barrels and they are sort of fussy (my experience) about bullet diameter, internal structure and composition. The bore is typically a little tight so the bullets aren't just "engraved" but lenghten a bit too. I'd suspect that standard rifling and barrels manufactured in that manner also seal the barrel by having a bore somewhat smaller than the bullet. So, the force required for engraving may be different by bullet composition (monolithic seem pretty prone to high pressures in polygonal rifling), bullet manufacturer, barrel rifling type and internal diameter. Looks like lots of variables to me. If you have a micrometer handy mic a few bullets from different manufacturers.

I've also noticed that the force required to engrave a bullet (and pressure) significantly changes point of impact for that particular series (LOT) of bullets. During testing with monolithic bullets my groups shifted horizontally to the left as pressure increases due to bullet size, shifted by several inches at 100 yards.

I can offer some direct information and some indirect information for you.

The force required to engrave an oversize bullet, say from engraving an 8mm (.323) bullet in an old 8mm (.318) bore only amounts to 500 psi or so. That was also stated about shooting a .323 bullet in a 30 caluber bore. So stated by one of the reloading authorities, not me. This was cited for several reasons, probably mostly to demonstrate that it is not as much as we think and that a slightly oversize bullet would not (alone) account for some blow-ups.

Back in the 1950s, when surplus ammo was very common, many shooters would pull the bullets from surplus ammo and substitute commercial hunting bullets of the same weight. The NRA, in their old loading book, tested this and found that the substitutions could give less pressure or anything up to dangerous pressure, depending on bullet brand.

I have the computer program "Quick Load." It is an interior ballistics program and works very well, indeed. It will predict good loads that agree closely with published data from manufacturers. It has allowance for moly coating and will predict a change in pressure based on brand of bullet. It takes into account length, bearing length, and so on. It must also have jacket thickness and toughness built into it, because it will predict that my .35 Whelen, when loaded with Nosler bullets, will give higher pressure than when loaded with Speer bullets of the same weight. This program also takes into account land and groove area, barrel length, actual bore size, actual land depth, and so on. What is even more suprising is that it will use average case capacity for brands and not fuss about it. It, however, estimates a teen bit lower than the loading books.

Maybe that is a help.

Geo,

That is the kind of information I am looking for. I assume that your comment about 500 psi was that this 500 psi is additional pressure required above what a non-oversize bullet would require. In that light it makes sense. I say this because 500 psi acting against a bullet in a 0.318" bore diameter only exerts a force of 39.7 pounds, hardly significant and one I apply by hand. I know I cannot push a bullet down a bore with my bare hands!

I have some information from an associate, but I need to get more details from him, regarding the measured force to push two different bullets through a 6" piece of 0.323" rifle barrel. I am not sure as to the number of lands and grooves, although I do know the rifling style is Enfield.

Bullet #1 (Sierra, I believe MK need to verify)
maximum force exerted to engrave riflings ~ 1200 pounds
sustained force after engraving < 50 pounds

Bullet #2 (Barnes X bullet)
maximum force exerted to engrave riflings ~ 2000 pounds
sustained force after engraving ~ 1000 pounds

As I indicated I need to get more details. I know he used a load cell in a hydraulic press to measure the loads applied to the bullet bases through a push rod fixture. I am curious as to the calibration condition of the load cell, as well as, the land / grooves used, the brand of barrel (I think it was a Shilen), the bullet weights and actual styles used, etc.

We talked about pressing some .416, .308, .458, and .510 bullets through barrel sections, but we first must get the barrels sections.

So if any of you have lengths of barrels (scraps are ideal as long as the riflings are to spec) around 6" or longer in those calibers and would like to know what force is required to push a bullet through these barrels let me know. You supply the cut-off barrel and bullets you are interested in (if they are the same as my selections then I will supply the bullets) and I wil supply the load data.

ASS_CLOWN

Indeed that was additional force.

Nope, don't have any extra sections of barrels, but wish I did just for the sake of contributing to an honest experiment.

Have fun, be safe, learn a lot.

Clown,



In his notes, the author of QuickLOAD hints he basically threw up his hands when trying to nail this one down. In the end, he simply used a bullet start pressure, as many others who've tried this game have done. I believe he drops the force to zero or some other small value once motion begins. I read some place he uses starting pressures which gave him decent correlation to piezo traces.



He uses 3600 psi for standard bullets and 6500 for both solid copper and FMJ with hard cores.



These are much lower than the 15 and 24 ksi indicated in the tests you cite.



Bullet jump (distance to the lands) has a big effect on this. He recommends adding 7200 psi to the above starting forces if the bullet is touching the lands.



He recommends dropping the forces by 1/3 if the bullet is lubed with compounds such as moly.



Throat angles will surely affect all this as well.



You might contact Steve Faber and ask him what he used. His NABM software included a model for bullet engraving. He no longer sells a commercial version and may be willing to discuss his "secrets". His site used to contain a list of the references he used.



As I mentioned in the other thread, this problem wrecks havoc on these simulators, and I feel it will prevent any of them from attaining pressure estimates to even 2 significant digits. Run through his calculations, his two assumed start pressures easily change the peak pressure 10%.



The article by William Davis in the NRA's excellent Handloading, c.1981, covering the effects of primer and bullet substitution was enough to convince me this is hopeless. Changing bullets of the same weight but using the same seating depth (this varies both jump and engraving force) causes pressure to cover the range from 44,500 CUP to 51,900 CUP in a .30-06. And this was with bullets of standard cup-and-core construction. Good luck!



I'd be interested in hearing more about your tests with the press once you get the numbers.

geo. & asdf,

If I can scrouge the barrel sections (which if left to me may take years that is why I asked if anyone had any scraps they wouldn't mind donating to the cause) it is my intention to share the results of the measurements. I will of course post pictures of the set-up and engrave as many different bullets as possible in groups of at least 10 so some statistical significance can be ascertained.

ASS_CLOWN

Would it take more energy to engrave rifling into a STW bullet going 4000 fps or the same bullet in a 7X57 going 2500 fps, all else being equal?

J

Ought to be the same.

For what it's worth,
Springfield Arsenal did some experimentation with hyper velocity projectiles in the '20s. The lab notes indicate that it takes about 1000 pounds of thrust to move a bronze projectile through a rifled barrel.

huntingcat,

We discovered that too, actually we recorded 1200 pounds with a bronze bullet (homemade) and a copper bullet (forget which alloy now). The actual force required to engrave the riflings seems to be caliber dependant, at least on paper. That is why I would like to get scrap barrel sections collected and do some testing, to discover if this is true or not.

ASS_CLOWN