I have a new article on Brinell hardness....

[C.F.Plinker]

If you are operating in the elastic region - pressures below 1422 times BHN - how much obturation can you get? For example, if your boolet diameter is 0.0005 below groove diameter will it obturate enough to seal the bore and prevent gas cutting? I can see where this would probably occur in the plastic region - pressures greater than 1422 times BHN - because you have enough pressure to deform the boolet permanently.

If you are in the elastic region how do you know if the alloy is strong enough to resist the forces acting in shear that are causing the rifling to spin the bullet? How does this relate to twist? Could a boolet that works in a Marlin 44 Mag with a 38" twist not have enough strength and strip the rifling or get gas cutting in a revolver with a 20" twist?

[Bret4207]

I'm going to reread what has been written here several times and see if I can put my observations into understandable words.

[Marlin Junky]

Bhn alone isn't the whole story.

Heck no, not to the accuracy equation; however, BHN* defines the boundary between elastic and plastic "states" pretty well. If BHN were the only variable, all this would be pretty easy but we really don't have (at least to my knowledge) a good way of measuring boolit coefficient of friction which would be dependent on alloy composition (e.g., ratio of Sb to Pb) and consistency. Boolit coefficient of friction would also be very dependent on BHN and chamber pressure (not to mention boolit lube) which would make things even more interesting, perhaps confusing to some and satisfyingly quantifiable to others.

MJ

* Note: BHNx1422, that is.

[BCB]

I printed the article to read a time or three as I can’t read articles that are lengthy on my computer. The screen is too small…

One thing that I really was glad to see was the fact the wheel weights aren’t the 10-12 now as they were years ago. I was thinking my SAECO tester was not so good. I continually get what Harry O indicates—7-9 most of the time. Now that’s not good as the older alloy would have been better I suppose, but it did verify my tester was O.K….

Good article…

BCB

[Gohon]

Doesn't mean anything except your tester is showing 7-9. Last batch of WW I smelted down was gathered about March of this year and my Lee tester read 11-12 but I do separate the stick on from the clip on type. I don't think any of the testers sold to the general public are all that accurate anyway if measured against lab equipment. Whats important to me is they are consistent.

Truth is I don't pay much attention to that stuff anyway. All I know is I'm running a gas checked 190 grain out of a 357 maxi at 2,100 fps and get no leading with great accuracy. I've pushed a 160 grain bevel base from the same gun at 1,600 fps with the same results. I haven't a clue what the pressure of those loads are.

[BCB]

Doesn't mean anything except your tester is showing 7-9.

Well, I disagree with that statement, but that is not the subject of this topic. Harry O certainly indicates that BHN us inportant...

I have never gotten 11-12 on any wheel weights with my SAECO. But I have gotten the 15+ with a know alloy of Lyman #2. To me that confires the SAECO is correct or at least would indicated it is accurate. Don't know anything about the Lee tester, but from what I have read about them, it may be a visual subjective (somewhat) decision as to what the actual BHN is. SAECO has lines that can be aligned and read...

BCB

[Gohon]

I'm aware of what the topic is about and I didn't mean to get it off track but you brought it up. On the other hand if one accepts what this thread is about then one has to know what the bhn is now don't they.

Go over to Lasc.us and there is a write up on BHN testers using Cabin Tree, Saeko and the Lee tester. About a dozen different individuals were selected with equal numbers of the different testers to test samples of a known BHN. Not a one of the individuals were consistent with others in the group. Some were off as much as 4 points of the known BHN. Only one of the three testers was consistent and close to the known sample.

That was my point......if what you use is consistent across the board then if doesn't matter if what you are using is not spot on.

[BCB]

Gohon,

I thoroughly perceive the demeanor of your response. And I completely understand your opinion and well expressed facts. And you have stated it a civil way that is truly not debatable, at least not by me…

‘Nuff discussed between you and me…

BCB

[Harry O]

If you are operating in the elastic region - pressures below 1422 times BHN - how much obturation can you get? ....

If you are in the elastic region how do you know if the alloy is strong enough to resist the forces acting in shear that are causing the rifling to spin the bullet? How does this relate to twist?

The slope of the stress strain "curve" in the elastic area is straight. The slope is called the Modulus of Elasticity. It is 2,000,000psi for lead. You can use this to calculate how much the bullet will shorten and then use that to calculate the obturation you will have -- but only up to the yield point. Beyond that, you cannot calculate anything with any accuracy.

Anyway, lets say you have a Bhn 15 mix and are shooting a 20,000psi .38 Special load (midway into the +P region). That is below the yield point so we can divide the pressure by the modulus. That is 20,000 / 2,000,000 = 0.010. This means that you take the original length of the bullet (front to rear) and multiply it by this number to get the length that the bullet will shorten. Lets say that the bullet is 0.700" long (a plain-base .38 Special semi-wadcutter). That means that under 20,000psi, the bullet will shorten by 0.70" x 0.010 = 0.007". It will be 0.693" long while under pressure.

That is change in length. How do we get the change in diameter? The change in length under loading is directly related to the change in diameter (90 degrees from the length) by a property known as Poisson's ratio. For lead, that is 0.431. (each metal has a different conversion number) That means that the change in diameter under 20,000psi of pressure is 0.007" x 0.431 = 0.003". That is more than enough to seal any leaks. I doubt that you could have a bullet 0.003" under, though. I have had no luck with undersized lead bullets. The pressure would escape between the wall and the underside bullet which would reduce the pressure and cause leading to boot.



The compressive yield strength of any metal is completely different from the shear strength for the same metal. Shear strength is always less than yield strength, but the exact percentage varies with each metal. In theory, the shear strength should be approx. 57% of the yield strength, but some metals are higher and some are lower depending on their atomic structure.

With lead, there is the same problem I mentioned about the yield strength. It varies all over the map depending on how the test was done. In any case, YES, the lead can strip out while trying to grip the rifling. Again, Veral Smith has some photos of this happening in his book. When this happens, the sides of the rifling are NOT parallel. There is a wider gap between the sides of the groove at one end than at the other. With shorter (or tighter) twist, there is a higher probability that the bullet will strip.

It would be possible calculate the the area of the side of the rifling times the number of grooves times the engraved length of the bullet and multiply it by the shear strength. That would be the maximum load that the bullet could take. The rotation of the bullet (which is the function of the twist and the speed) can be used to figure the force exerted. I have never actually done it and my guess is that the variables would make it pretty much impossible to get a very accurate figure. In most cases, however, if you stay below the yield strength, you should not have any problems with the bullet stripping out. With a VERY short twist (such as a full power load with a 160gr 6,5x54 Mannlicher-Schoenauer bullet in a barrel with one turn in 7.87"), that may not be the case, however. Sorry I cannot be more specific on how to calculate that.

[Harry O]

Doesn't mean anything except your tester is showing 7-9.

That is why the industrial testers I had a work had specific plates (very high priced plates I might add) that were a known hardness and they were used to periodically check the accuracy of the testing machine. I have not seen that done for ones being sold to bullet casters.

What I did for my private testers was take a stick of "pure" plumbers lead and I check my instrument against it from time to time. I still have a lot of room to run more tests on it. I have not had my testers change from one time to another using the same piece of lead. I have had 4 different hardness testers and still have three of them (I traded the SAECO one for a set of 41 Long Colt dies).

The WW's when I started casting about 20 years ago were definitely harder. The ones I get now are less hard. It means I have to add more monotype and tin to get the hardness I want. I just got about 150lbs of truck weights, though, and they are much harder (Bhn 11-12) than the most recent car WW's. They are so huge, that I have no doubt they need more antimony to keep them from flexing until they break.

[Ridgerunner665]

That article mentioned 18 wheeler WW"s...

I'm a truck driver and I have a few big truck WW's...he's right, they make those 1/2 ounce car weights seem microscopic, and the truck WW's are harder...I don't have a BHN tester yet, but i can tell that by squeezing them with pliers.

An 8 ounce truck WW...


Not many places have truck WW's though...most drivers and companies have gone over to using the CentraMatic wheel balancers
( http://www.centramatic.com/Home.aspx )

[Bret4207]

Anyway, lets say you have a Bhn 15 mix and are shooting a 20,000psi .38 Special load (midway into the +P region). That is below the yield point so we can divide the pressure by the modulus. That is 20,000 / 2,000,000 = 0.010. This means that you take the original length of the bullet (front to rear) and multiply it by this number to get the length that the bullet will shorten. Lets say that the bullet is 0.700" long (a plain-base .38 Special semi-wadcutter). That means that under 20,000psi, the bullet will shorten by 0.70" x 0.010 = 0.007". It will be 0.693" long while under pressure.

Doesn't that make the assumption that the entire boolit obturates? Again, in my experience, that doesn't always happen. And wouldn't the design of the boolit play into that? A bore rider with less bearing surface might start moving easier than a full body boolit and have less time for the pressure to affect it?

[Harry O]

Doesn't that make the assumption that the entire boolit obturates? Again, in my experience, that doesn't always happen. And wouldn't the design of the boolit play into that? A bore rider with less bearing surface might start moving easier than a full body boolit and have less time for the pressure to affect it?

You are correct that the bullet does not act uniform from front to rear at the same instant. The numbers I used are an average. The effect will be greater where the pressure is applied at the very rear of the bullet) and zero at the very front of the bullet. However, the average will be the same as what I used.

[BABore]

Do the lab tests enclose a lead boolit in a cylinder that is 0.001 to 0.003" smaller in diameter? Are the lube grooves filled with a non-compressible substance like boolit lube? Is the pressure applied in milliseconds at the start, then backed off? Is it done to proper simulate the forward motion of the boolit as happens in the bbl?

With a Welding Engineering degree and many metallurgy, Statics, and strengths of material courses under my belt, plus almost 30 years of experience, I understand and appreciate the subject here. I also understand that lab conditions and controlled tests do not always reflect life in the real world. Boolit hardness can be acheived from many directions. Linotype alloy is around 22 bhn air cooled. 50/50 WW-Pb, water dropped, is 22 bhn with my WW's. A 35/65 WW-Pb alloy with an addition of nickel babbit, water dropped, is also around 22 bhn. All the same hardness, yet do they shoot the same? No, not at all. Do they expand the same? Not even close compared to lino. Run any of these alloys up over 2,500 fps and your over your hardness limits in some cases, yet they behave very differently. Why? Cause there's more going on here than just a Bhn number. Boolit fit to the case neck, throat, bore, and groove as well as bore condition all come into play. How you launch the boolit is critical. Do you hammer it hard out of the gate, do you get it into the bbl a bit and hammer it, or do you get it into the bbl and gradually increase pressure til it peaks? Gas check shank length? Is it a stepped shank? How deep, how long? Size, depth, and position of the lube groove(s). All this has an effect in how it happens in the real world. Why does my 44 SBH shoot a 10 bhn boolit with the best accuracy at full pressure and velocity? Why does my 41 SBH only do the same with 22 bhn boolits? Why does my 480 Ruger SRH allow me to shoot a mixed cylinder of 10 and 22 bhn, plain based boolits to the same fine accuracy of either one individually? At 48 kpsi? To the same POI no less. Why is it that I know many serious casters that can do the same things that are outside the lab?

IMO, hardness is just a number. I know its meaning and know how to get there. I also know how to cheat the hardness/pressure formula in many cases. It's something I keep on file to use to my advantage when needed or desired. It's not something I fence myself into and marry.

[Bret4207]

Thanks BA, you put it far better than I could. No offense to anyone involved, it's just that there's more going on here than just a Bhn.

[45 2.1]

Thanks BA, you put it far better than I could. No offense to anyone involved, it's just that there's more going on here than just a Bhn.

And a formula that can be beaten by several people here.

[odoh]

Is the http://www.sixshootercommunity.com/h...etcasters.html link working for others? I get msg server is down ~ from http://guide.opendns.com/main?url=ww...rcommunity.com

Seems like this is a meaningful thread . . . worth following

[mrbill2]

I wanted to read this thing, but the link it's not working.

[onesonek]

Well,,,,,I understand the engineering mathmatical science behind the bhn/pressure thingy. But while new to casting, with 35 +yrs of reloading behind me, one thing I have learned,,,,,there seem to be no absolutes. I can readily see and understand Bret's and BABore's points.

[357shooter]

Added later: Everything I write say and think is limited to revolvers, specifically 357 magnums.

The engineering and math is fun to read about and for discussion. However taking it to the range an validating something like "matching pressure to BHN" to me is the tiebreaker and either validates the concept or not.

The only reason I even bring it up is there are enough articles an books about this that get read and then recited as truth. Sometimes here, often on other boards, many people are trying to figure out whats wrong with their gun because of their bad results at the range.

I don't claim to be able to explain all that happens to the bullet, and actually don't really care that I can't. I have proven beyond any shadow of a doubt that, first, the most accurate boolit in my 357 magnum is:

30,000 PSI with BHN 7-8 (< 1inch groups)

The most accurate BHN with other pressures (slightly bigger groups by .25 to .5 inch bigger at 25 yards, <1.5inch groups) are:

10,000 PSI with BHN 7-8
20,000 PSI with BHN 7-8
34,000 PSI with BHN 7-8

Also added later: other BHN opens the groups and are less accurate for each of these loads. The harder/higher the BHN the bigger the groups.

This is a rhetorical question: Shouldn't the results speak for themselves. I'm not claiming that BHN 7-8 is the most accurate alloy in every gun, and agree that there are many other factors are at play.

I'm not trying to disrespect anyone or be rude, but I do think the several thousand boolits of testing across alloys, moulds, OAL, etc... did provide a result that is valid. I also acknowledge that starting testing after reading the Lee book and accepting this "matching connection w/pressure" concept as valid caused me to spend many hours and many boolits trying to figure out what was wrong with my boolits, my gun, or my casting approach. In hindsight it was a good learning experience. But I wish someone just let me know up front...

I'm hoping to add to this discussion, not drag it down as this site is where I've learned to cast and have respect for all the folks here.