Following is what Larry Gibson posted in a thread over on the castboolit forum. Here's the link to see it's entirely:

http://castboolits.gunloads.co...lits-pressure-limits

I picked out the following posts from him:

There are serious flaws with the conversion formula posted above. It is not reliable. Denton made too many incorrect assumptions and used data from different sources to come up with that formula. There is no reliable conversion formula between CUP and psi. One can make a close presumption IF one has the CUP and psi data of one load taken at the same time. That does not mean the pressure data printed by "close" loads in different manuals or from different sources will give you reliable information/data for any sort of conversion of CUP to psi or visa versa. One can quickly get into dangerous pressure range using that formula interpolating data from various sources. I suggest it not be used. My comments here are derived from what most all ballisticians say who actually measure pressure and my own experience having measured the pressure of thousands of different loads in a multitude of cartridges.

The basic problem with Lee's formula is two fold. First he was seeking to answer the age old question of why accuracy went south at a certain level of velocity/pressure. The solution he came up with is only partially correct in a round about way. What he missed in his theory was/is the adverse affect of RPM at a certain level, especially with cast bullets. That is evidenced in his manual where Lee misinterprets the results "John" got in a test with a 10" twist 30-06 and one of Lee's cast bullets. The reason accuracy in the test was lost where it was was not because of too much psi but because of too much RPM.

Secondly the "constant" in his formula is based on the elastic limit/yield strength/tensile strength of pure lead for simplicity because every binary/ternary alloy, depending on the percentage of metals, will have a different "constant". Since he/we don't exactly know what the elastic limit/yield strength/tensile strength is of the alloy we are using Lee used the one for lead by default. Thus using that constant for pure lead gives the lowest psi where the bullet will supposedly "fail" and accuracy is lost. Since binary and ternary alloys are "harder (they basically have better grain structure which strengthens the alloy) they can stand a much higher psi depending on the strength of the alloy. That is the primary reason Lee's formula does not work most often; the constant is incorrect as binary and ternary alloys stand up to much higher psi than the formula indicates. Like many things though, the formula, does seem to work once in a while which gives some a false sense of reliability in it.

As a quick example; I regularly shoot bullets cast of #2 alloy to 2900 fps in my 30x60 XCB holding consistent moa accuracy to 600 yards and to 2700 fps with 1 1/2" moa accuracy in my 308W Palma rifle. The loads run a measured 50,000 psi +/- in each rifle as measured with the Oehler M43 PBL. According to Lee's formula that bullet cast of #2 alloy is supposed to "fail" with accuracy lost at 30 some thousand psi yet that does not happen. So how is it possible I'm shooting them with excellent accuracy at high velocity with 50,000 psi? The reason is both barrels have slower twists which keep the RPM under 140,000...... that's where Lee went wrong, he didn't understand that many cast bullets are much more adversely affected by RPM than they are of psi. I can give you many, many more examples that disprove Lee's formula not only my own but what many others have also found.

With that being said, don't get me wrong. I like Lee's products and certainly respect the man. I have and use quite a bit of Lee's products. However, Lee's max pressure formula is a dog that just doesn't hunt.

"I(n) the Lee book page 136, they show an example of there testing.
As it starts wit a low pressure load and work up you see the accuracy gets better. Then at a point just below the psi of the bullet is the best group. It then opens up once you get above that pressure."

Lee's friend John (who conducted that test according to Lee) used Linotype alloyed bullets and achieved the best accuracy at 24,838 psi (assuming that to be a calculated psi as CUP, transducers nor strain gauge measurements are not that finite). Yet I, and numerous others, push softer alloyed cast bullets to 3,000 +/- fps at 50,000 +/- psi (actually measured, not calculated). Lee's formula and book says that should not be possible as the bullet should have "failed" because of Lee's calculated "compressive strength" of the softer alloy we use.

Again, as stated earlier, Lee failed to consider the adverse affect of RPM and the fact that a constant for pure lead gives a much lower value to the actual psi a ternary alloy can withstand. Those of us who do shoot ternary alloyed cast bullets at high velocity in the 2400 - 3000+ fps range understand that controlling the RPM via slower twist barrels is the secret along with properly designed cast bullets cast of excellent quality. The level of psi we push to far exceeds what the formula says is possible or Lee's further explanation on page 136.

Fact is Lee doesn't get to the same place because the psi of the load was only partially responsible for the loss of accuracy at the velocity attained in John's test. John pushed the RPM threshold by using a well designed bullet and probably a medium or slower burning powder. Lee doesn't say which of his bullets John used but we do know that the C309-160-R and the C312-160-2R shoot very well at higher velocity as they have attributes of design for that level. Those two bullets along with the C312-185-2R have successfully been pushed much higher in 12 - 14" twist barrels also at much higher psi than at the point of "compressive strength" that Lee's formula says where they should fail.

Lee's formula follows the old assumptions as to why accuracy is lost at a point with cast bullets. We now know those assumptions were not correct.

My ternary alloy is Lyman #2 [90-5-5] alloy. After considerable testing of different alloys in several different bullet designs and in 10, 12 and 14" twists barrels (all 308W) I found Lyman #2 alloy to give the best in casting quality and accuracy at HV. I also conducted an extensive test of many lubes (commercial and home made....supplied by others) and found Javelina and White Label 2500+ gave the best accuracy at high velocity....2600+ fps. After success with the 14" twist I had the 30x60 XCB rifle built with a 1-16" twist to attain 3000+ fps with a 164 gr 30 XCB bullet.

The "sweet spot" I found and others found is to keep the RPM under 140,000. I have never lost accuracy to any cast bullet coming apart from too much spin because accuracy is lost well before that when to cast bullet exceeds it's RPM Threshold. I have many times demonstrated and explained how accuracy is lost when the bullet exceeds the RPM Threshold. Using large targets at 200 and 300 yards to capture the non-linear expansion (read that loss of accuracy) it is found the bullets are still stable and have not come apart. That is because the bullet holes were all observed/accounted for so all bullets made it to the target and all the bullet holes were perfectly round of caliber size demonstrating the bullets were perfectly stable.

Granted "tensile strength" or "compressive strength" of the alloy does come into play somewhat and helps establish the RPM Threshold for the bullet/alloy and load used. However, what was proven conclusively was that when the RPM was kept under 140,000 the bullets "tensile strength" or "compressive strength" was never an issue even upwards of 50,000+ psi. I have demonstrated that by shooting many 10 shot moa groups out to 300 yards and even out to 500 and 600 yards with the 14" twist rifle at 2700 fps and the 16" twist rifle at 2900+ fps.

Also the original test objective was to see how fast a ternary alloyed cast bullet could shot and maintain 2 moa or less accuracy with linear group dispersion to 300 yards. That accuracy goal was exceeded with moa accuracy being consistent with 10. 12, 14 and 16" twist rifles. All loaded to 48 - 50,000 psi. Of course the highest velocity with 1 - 1/12 moa accuracy was dependent on keeping the RPM under control. I have also demonstrated with a 10" twist 308W how the RPM Threshold can be pushed up and still maintain 2 moa accuracy at 500 yards. None of those accomplishments would have been possible had we adhered to Lee's formula.

***
What the writer of this fails to understand, although he believes he does, Is it's not the rpm, but a combination of factors that influence the bullet while inside the bore. These factors exceed the alloys yield, torsion and shear strengths distorting the bullet from the time it starts moving until it is totally engraved by the rifling. Depending on whether the bullet fits properly (few do as most are undersize in several spots) the trip down the barrel, if centered properly will give excellent accuracy or if the bullet tilted while entering the rifling results will be poor with worse accuracy. Velocity alone or with a combination of very fast rifling adds little effect to these factors. The writer always dictates the rules for HV CAST ACCURACY which morph depending on what he reads next or learns from somebody else. His testing is flawed ...or better said he is misinterpreting those test results) that one cannot use powder coat (most recently added to his dictations) paper patch, or copper in the alloy always limiting others to a binary or ternary alloy. You know why people? Because you can paper patch, powder coat, add copper to the alloy or heat treat a suitable alloy to much greater hardness and exceed his unproved RPM theory.... that's why. His method is one way to shoot high velocity (and rather expensive to achieve), but not the only way. There are a lot of people on the forums that do as well or better... cheaply and at less cost than what he purports. Also, the technical terms he uses and abuses would not fly among the people that actually know what they mean and their uses. The narrative above leaves out many terms and missuses most of what is there. As for tensile strength of lead that these people use, it is out of place and seriously misused.... lead is not under tension at any time in a firearm..... it is under compression while under going torsion and shear while going down the barrel. Misuse of terminology remind me of a high school dropout that just reads a little to get terms to impress people. This alloying information has been in print for a long time, but one has to understand it to use it to your advantage.

Larry is aware of this, but he just can't put the two together and comes up with his looks good always changing RPM Threshold Theory and that is exactly what it is and all the people over there that follow and worship him because they don't know any better.

An accurate post as usual Vince. Shooting cast bullets at higher velocity would be a whole lot easier if we didn't have several people beating there own horn and running others down.

I wonder if he has ever captured a bullet and looked at it.

He captured bullets from his 30 XCB into wet newspaper, or some kind of wet paper, at distance. Although he though they looked good there are strong evidence that there was severe gas cutting. I don't think he noticed it. Let's just say they didn't look like a fired bullet with nice rifling grooves cut into them. There were a lot of smeared areas and the gas cutting. If I remember the alloy was very hard. Don't forget Bjorn was shooting Linotype until his started eroding his throat away....which he was told that would happen by Bob and Joe.

I quit visiting and posting on Castboolits several years ago. What LG posts, thinks, does or does not do, I could care less. Would forget he even exists if it were not brought up on this site. His activity bothers me none.

I must say, I wince at the personal attack mode of communication. Too much of that going on everywhere for me want to read on a hobby forum. While the negative analysis of something is useful, the positive presentation of the alternative is better. I would love to see a thoughtful presentation of how RPM is not a barrier because...
I can see how RPM can really trash a trashy bullet, a trashy throat, a bad bore, no lube, and a bad powder column reaction but my gut says RPM is not the original causative agent, it just an agent that exacerbates the flaws.
I can tell from reading that you know what your talking about. I would love to read about your solutions for good cast shooting.

Fury I think you actually got a good handle on the issue.

get that bullet straight dead in the middle of the barrel and don't damage it when you launch it.
the first 1/2" of movement is the most critical.
there is other stuff such as dynamic and static fit that make a big difference.
but you have to have the straight start or nothing else matters.
powder is down the list pretty far and is used in conjunction with alloy make up to get those other little bits and pieces of more speed and better groups.
start with the centerline first then work on design, then on alloy powder combinations.
and finally you can tweak things just a bit more with the viscosity of your lube.

that's is how you get from 1500 fps to 2500 fps.

quote:

Originally posted by Fury01:
I must say, I wince at the personal attack mode of communication. Too much of that going on everywhere for me want to read on a hobby forum. While the negative analysis of something is useful, the positive presentation of the alternative is better. I would love to see a thoughtful presentation of how RPM is not a barrier because...
I can see how RPM can really trash a trashy bullet, a trashy throat, a bad bore, no lube, and a bad powder column reaction but my gut says RPM is not the original causative agent, it just an agent that exacerbates the flaws.
I can tell from reading that you know what your talking about. I would love to read about your solutions for good cast shooting.

Fury you are exactly right. Just trying to make shooters see this fellow pushing this RPM is totally wrong. Like Lamar said get everything right RPM doesn't figure it...to a degree. We're finding really fast twist does something to the cast bullet, even if the bullet is near perfect and started into the bore straight, that's what we are working on. Some of the issues are shallow groove depths. The bullets aren't stripping and I've never seen any evidence of that in rifles. Seen a lot of it in revolvers. I think we all know why in revolvers.

Glad you posted and posts like yours is a step in the correct direction.

quote:

Originally posted by carpetman1:
I quit visiting and posting on Castboolits several years ago. What LG posts, thinks, does or does not do, I could care less. Would forget he even exists if it were not brought up on this site. His activity bothers me none.

well, i heard awhile ago that LG was some kind of god in the world of cast bullet shooting over on Castboolits

quote:

Originally posted by john c.:

quote:

Originally posted by carpetman1:
I quit visiting and posting on Castboolits several years ago. What LG posts, thinks, does or does not do, I could care less. Would forget he even exists if it were not brought up on this site. His activity bothers me none.

well, i heard awhile ago that LG was some kind of god in the world of cast bullet shooting over on Castboolits

A false God!!!!!!!!!!!!

I find it most curious that one would get so worked up about a persons opinions on another web site.

Easy solution I have found works well, is either don't go to a site or to not follow a posters posts.

Maybe it is just not as simple than I understand it to be.


OK, what did I do with those Nomex/Kevlar Long Johns!

quote:

Originally posted by TCLouis:
I find it most curious that one would get so worked up about a persons opinions on another web site.

Easy solution I have found works well, is either don't go to a site or to not follow a posters posts.

Maybe it is just not as simple than I understand it to be.


OK, what did I do with those Nomex/Kevlar Long Johns!

He has perpetuated his myth theories all over the internet and has been the sole reason many many people were banned from such forum. Yes you really don't understand. His theory is a hindrance to new cast shooters. But like I said in another post here lets try find out what the real culprit is with fast twist rifling...can you do that TC?

I just cast and shoot my cast the way that works for me and read how others do it for alternative opinions.
What works for me the way I do it works for me and that makes me all warm and fuzzy!

quote:

Originally posted by TCLouis:
I just cast and shoot my cast the way that works for me and read how others do it for alternative opinions.
What works for me the way I do it works for me and that makes me all warm and fuzzy!

.....but TC if you shoot high velocity from fast twist barrels and it works for you I sure would like to listen to what you do and I imagine other's would to. Please don't post that you have no use for that because there is indeed a use for it. Maybe not what you need.

quote:

Originally posted by vzerone:

quote:

Originally posted by TCLouis:
I just cast and shoot my cast the way that works for me and read how others do it for alternative opinions.
What works for me the way I do it works for me and that makes me all warm and fuzzy!

.....but TC if you shoot high velocity from fast twist barrels and it works for you I sure would like to listen to what you do and I imagine other's would to. Please don't post that you have no use for that because there is indeed a use for it. Maybe not what you need.

too much science, too little fun

quote:

Originally posted by TCLouis:
I just cast and shoot my cast the way that works for me and read how others do it for alternative opinions.
What works for me the way I do it works for me and that makes me all warm and fuzzy!

this!

quote:

Originally posted by john c.:

quote:

Originally posted by vzerone:

quote:

Originally posted by TCLouis:
I just cast and shoot my cast the way that works for me and read how others do it for alternative opinions.
What works for me the way I do it works for me and that makes me all warm and fuzzy!

.....but TC if you shoot high velocity from fast twist barrels and it works for you I sure would like to listen to what you do and I imagine other's would to. Please don't post that you have no use for that because there is indeed a use for it. Maybe not what you need.

too much science, too little fun

Actually it's not.

it's actually rather simple.
don't EFF things up.
don't use lyman molds.
don't try using more 4895 than the bullet can take.
don't use a bore ride bullet.
don't use a 2 diameter parallel sided bullets. I.E. pretty much 99% of every mold lyman ever made.
the other 1% are the ones they dropped.

start them straight in the barrel and accelerate them no harder than the alloy can withstand.

none of that seems very hard to me.
do any of the dont's and suddenly there is this magic bullet failure to fly straight.

Good job Lamar. That should tell the non science people here what not to do. The main problem is they won't learn enough to be able to do it from copying certain others.

quote:

Originally posted by 45 2.1:
Good job Lamar. That should tell the non science people here what not to do. The main problem is they won't learn enough to be able to do it from copying certain others.

They sure as hell won't learn it from the CBF Guru!! He deliberately rigged the 6.5 Swede test for a failure. Right 45 2.1?

Yep...he used the procedure I said wouldn't work.

quote:

.....but TC if you shoot high velocity from fast twist barrels and it works for you I sure would like to listen to what you do and I imagine other's would to. Please don't post that you have no use for that because there is indeed a use for it. Maybe not what you need.

verzone
Funny I never mentioned velocity or twist rate but you were able to leap out in a single bound assume that from far too little input of information.

Oh well back to doing stuff my way and reading what ALL of the experts think.

AND

That's enough of this interweb jousting for the year.

quote:

Originally posted by TCLouis:

quote:

.....but TC if you shoot high velocity from fast twist barrels and it works for you I sure would like to listen to what you do and I imagine other's would to. Please don't post that you have no use for that because there is indeed a use for it. Maybe not what you need.

verzone
Funny I never mentioned velocity or twist rate but you were able to leap out in a single bound assume that from far too little input of information.

Oh well back to doing stuff my way and ignoring ALL of the experts.
Enough internet jousting for the year

T C please notice the biggest two letter word "if"!!!