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Yes, I agree, but then you should also take into account
the dimensions of the bullets, the fact some are tapered so only a small part of the bullet is engaging the rifling plus a whole lot of other factors.

Exactly, something planned.


As an example, I have fired "hard" Woodleigh Steel jacketed solids through a heap of double rifles and none have OSR.

I'm not certain Woodleighs would be the only steel-jacketed solids falling under the "hard" tag. For example, what would be the effect of a lifetime of shooting, say, Hornady's, in a gun with thin, soft UNDER-sized tubes? I'm not sure, but it wouldn't seem like a good idea.

Just how "hard" is "hard"? I don't know, but if anyone wants to attack THAT problem, have at it. I believe a slick little device could be made to measure the resistance of a bullet to rifling. I'm going to guess that a similar device exists for some reason in the world somewhere, but I don't know where or what it is. The machinists here might be able the weigh in on that one. Might be nice to have some means by which "resistance to rifling" could actually be compared.

Use Woodleigh's hydraulic test as an example. Could a small device be made to measure such resistance? I think so. Would it be relevant to the discussion? I don't know. Maybe, maybe not. It would not necessarily correlate to exactly what is going on in the barrel under the pressure of the expanding powder gases, but might be a useful measure of bullet "hardness" for comparative purposes.

PS: I make knives so I'm well acquainted with the various methods of measuring material hardness. Let's not confuse material hardness here with "hardness" as it might apply to resistance to rifling. For example, a Woodleigh steel jacket solid might scale a higher hardness to a Rockwell instrument yet might slide through rifling easier than some other bullet, or maybe not. Just some further brainstorming...

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1. Chamber pressure is not necessarily related to pressure in the barrel. The pressure curve of monometals may be different than a conventional lead core bullet. In my experience, Barnes bullets are more accurate when they are seated rather deep, giving them more jump to the obturation of the rifiling. Maybe the pressure curve is occuring farther down the barrel than a FMJ?

As an example I am familiar with, when the USMC switched from 5.56mm M193 ammo to heavier SS109/M855 two problems occured. The diameter of the gas port had to be substantially reduced as the pressure curve was much higher at the gas port w SS109 than M193.

the other problem was w SS109 ammo itself. The hard (Rockwell C70) 10 grain steel insert in the ogive made contact with the rifling, just barely, but enough to wear out barrels in just 5,000 rounds. (No lead sheath protected the bore like conventional AP or API ammo). FN originally thought this was due to the high cyclic rate of the Minimi (later M249), but same problem occurred in XM16. Since XM16 had 3 shot burst it wasn't a problem of cyclic rate. A bit more lead in core and pushing the penetrator farther forward did the trick. Yet chamber pressure was normal NATO specs. And it wore out barrels. OSR was not a problem even in relatively thin M16 barrel.

2. Tank barrels are smooth bore so no relation to OSR there from ordnance world.

3. Light weight artillery barrels have been adopted for both 105 and 155mm howitzers. Since artillery shells use soft copper driving bands OSR was not an issue. Most weight was saved from carriges rather than barrels, which went from 39 caliber length to 42, 45 and even 52 calibers in length.

20mm Gatling gun barrels are really skinny and OSR is not an issue I am aware of and I have tested many GE products. i have also tested three light weight 0.50 and 12.7mm HMG's and it has not been an issue w AP and API ammo.

4. It is interesting that Barnes chose to use a teflon based product on their original blue 470 bullets. And they dont need to do that anymore with the banded bullets. That thick coating was surely for a reason and was basically a synthetic copper jacket.

5. the original Thunderbird Cartridge Company (TCCI) patent for brass monometals used the 0.50 BMG ctg as proof that the turned bullet had less pressure than a copper coated steel jacket with lead core 0.50. (See #1 above). the Barnes and TCC bullets I used in my 450 Dakota required less powder to reach similar velocity than FMJ's. However the original Barnes slimed my barrel so badly I would never recommend them to anyone. The banded bullets are much better.

6. Mike Brady the founder of North Fork may have something illuminating to say about this issue if he has the time or interest to do so.

In conclusion, I suspect that OSR in double rifles may be related to the difference in pressure curve of a monometal vs a FMJ.

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I am registered now. Thanks Mike for posting my notes above. I might add that the only OSR like issues I am aware of came from over heating of a very lightweight medium machinegun barrel, the 19 pound M60E3 which actually had barrel droop after about 500 rounds. I know DR barrels get very hot, my 12 ga Birmingham SS shotgun certainly does. Maybe that is also involved???

Andy

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That's right - no color or light phase at five hundred degrees Fahrenheit.

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Actually, with the simple carbon steel alloys I use, and polished bright {or even "well struck" }, 500 gives oxidation colors of purple/blue.

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What are the Rosary, the Cross or the Crucifix other than tools to help maintain the fortress of our faith in Jesus Christ, the Son of God?

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9.3-


I meant to say from a blacked barrel you won't see a color change and it won't glow.





Cheers
Tinker

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IMO, I doubt that soft steel or overheating/annealing have anything at all to do with OSR.
If lack of barrel hardness is a contributor, degradation of the rifling inside the barrel would become apparent long before OSR. I would think that for OSR to occur, the lands would have to actually be harder than the rest of the barrel steel.
I will have to re-read this entire thread, but is it right that OSR is visable but not measurable?

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I discussed this very question with Graeme Wright. His explanation to me was that the shadow effect is of course caused by a change in dimensions, tho they may be less than .001" which is the limit of common micrometers available to hobbyists, shooters, handloaders etc. This makes sense since it would seem at least inuitively that anything that can be seen with the naked eye can also me measured, albeit with proper instruments.

As for interior dimensions, trying to mike slugged bullets to less than .001 is admittedly somewhat difficult depending on rifling type so I can imagine miking interior dimensions might produce mixed results. But it should be able to be accomplished, especially with the gross damage results commonly described. At the very least, it seems reasonable to suggest that some dimensional change would be noticeable in the inside if there is any visible change at all on the outside.

Regardless, with all the discussion of the topic on this site, no one has as of yet posted on this site slugged bore dimensions before/after OSR has occured to a gun.

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By not measureable, I meant by us amateurs.

I am sure if you had scientific instruments or lasers,
then yes, you could measure both the internal and external
dimensions.

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You might be right as to requiring very fine instruments.

I really have no idea what instruments might be needed. As we all know, damage caused by hard bullets is described as ranging from faint shadows of pressed out rifling all the way to spitting of rifling out the muzzle, ribs falling off, etc.

Some of the latter would, I think...be measurable with a ruler and weighed by the pound...

But no pictures of the latter types of damage have been posted here, either.

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What are the Rosary, the Cross or the Crucifix other than tools to help maintain the fortress of our faith in Jesus Christ, the Son of God?

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