Bullet hardness questions. MBC, please weigh in.

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I didn't realize reloading was MUCH more art than science.

I don't think it is, I just think we don't understand all of the science involved. I think we've got a good handle on most of it, but not all. I'm not sure we will understand it all completely until we get some high-speed cameras inside the chambers.
 
There is both art and science to this and also, where they meet, there is voodoo! :)

Gadzooks, you are absolutely correct about P.S.I. versus C.U.P. This is one of those "to-do list" things that I need to correct.

Oto, I actually didn't state that going with the correct hardness would result in no leading, rather, that leading can be minimized this way. As has been pointed out by the wise folks here, other factors are very important in this equation, especially bullet/barrel fit, which is the most important factor in my opinion.

I used the 5.0 grain Bullseye load as an example and used round numbers to exemplify the concept. Other powders will create more pressure, some less. But it serves as a good example on how to do the calculation. And also, I was reporting on customers' experience, taken from this very forum, when I mentioned the 1450 fps/no leading. I don't actually own a .357, myself.

You mentioned that I made a big deal about the hardness, well, that would be because that is the only real variable that we can control and so that is what we focus on. If you would visit our Facebook page (linked to from our website) and look at the Discussion area, you will find more specific information that what I put up in the Technical article on the main page.

But that said, obturation IS important and can compensate to some extent for an oversized bore and, all things being held equal, it will minimize leading.

Brad
 
Every once in a while someone comes along who understandable thinks we can lay out everything about leading in a scientific way so that we can figure out in advance what alloy or BHN we need for a certain application.

They soon find out there is no magic formula, or set BHN number for any given application.

There are so many variables in alloys, BHN, hardness, how ductile it is, dimensions and smoothness of throats and bores, peak pressure, pressure duration, powder speed, etc, etc, that each case has to be tried on its own.

We do have some very good proven facts that help us formulate a load that "should" work without leading in a given application, and then help us eliminate any minimal leading if we get it.

But yes, there is art to it, as well as science. :)
 
When I transitioned from 21-24 BHN hard cast bullets to Missouri Bullet with 12-18 BHN, I found these articles by Glen Fryxell to be quite enlightening:


Cast Bullet Alloys and Obturation - http://www.lasc.us/FryxellCBAlloyObturation.htm
... there's not really much need for ALL cast bullets to have a Brinell hardness of 24 ... In fact, these hard bullets may well be inadvertently causing leading. How? These commercial alloys are commonly too hard to "bump up" (or obturate) and seal the bore at typical revolver pressures. The resulting blow-by of the hot gases past the bullet's bearing surfaces can leave significant lead deposits in the barrel.


A Few Comments on Cast Bullet Alloys - http://www.lasc.us/FryxellCommentsCBAlloys.htm
There are very, very few revolver applications that require a BHN of over 20. In my experience, revolver leading can almost always be traced to some other factor (inadequate lubrication, improper sizing, barrel/frame constriction, etc.). Only very rarely is barrel leading caused by the bullet being too soft. In support of this claim, let me point out that many muzzle loaders prefer bullets cast from 30-to-1 alloy (which is quite soft, BHN of about 9) and these smokepole slugs are routinely driven to 1300-1400 fps. In addition, high-velocity .22 Long Rifle ammo uses an even softer bullet at over 1200 fps (and if a .22 leads, it's a gun problem, not an ammo problem). Elmer Keith's favorite cast bullet alloy was 16-to-1 lead/tin, which has a BHN of only 11. This is the alloy that gave a roaring birth to the .44 Magnum using plain-based cast bullets loaded to 1400+ fps. Properly loaded and lubed, Elmer's alloy will leave a magnum revolver barrel shiny and clean after a long day shooting.


Lubricating Cast Bullets - http://www.lasc.us/FryxellLubeCastBullets.htm
Undersized cast bullets leave a gap between the bullet and barrel, leaving them unable to restrict this pressure-induced lube flow. As a result, the lube very quickly gets blown out of the barrel in front of bullet, leaving the bullet "naked", un-lubricated and unprotected. This phenomenon is especially problematic with the hard lubes; once molten, the low viscosity liquid lube gets blown out rapidly if the bullet is undersized.
 
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