Cast psi calculator

[sutherpride59]

Without specific load data is there anyway to calculate the PSI generated in a cast load based off of copper jacketed data? I know this isn’t most important thing in the world But it would be nice to be able to guesstimate how much psi is going to be on my cast bullet based off a jacketed data.

[Rcmaveric]

Richard Lee's modern reloader 2nd edition has a chapter on estimating pressures from some of their load data when listed.

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[Larry Gibson]

Without specific load data is there anyway to calculate the PSI generated in a cast load based off of copper jacketed data? .......

No there isn't,

[sutherpride59]

Hey Larry is back! Welcome back Larry! Yah that’s just a chart showing how much psi the bullet can take of that powder at a certain bhn. It’s a good reference but doesn’t really provide what I’m looking for. I’m just curious if there is a formula to guesstimate the pressure based off a known recipe.

[GhostHawk]

I suspect too many variables for that to work.

[Larry Gibson]

I suspect too many variables for that to work.

Correct.

[mdi]

Would Quick Load provide any information on pressures?

[Larry Gibson]

The OPs question was;

is there anyway to calculate the PSI generated in a cast load based off of copper jacketed data?

Quick Load is different. QL can give a fairly close estimate IF all the requested data is input correctly. Leaving data out, estimating data and inputting incorrect data will seriously negate the accuracy of QL to estimate pressure.

[fivefang]

Hi Larry, in the late 50's I did not have a Chrony, but shot my Ruger .44 mag. with the 215 gr. Thompson GC. bullet over 27.5 gr.Herc. 2400, back then I wanted to duplicate the factory load, did I come close? & thank you for alof the past comment's , Fivefang

[Larry Gibson]

Be a couple months before I can answer that question. Haven't tested 2400 under that bullet but actually have it on my "to do" list for this fall.

[lotech]

When these questions come up, I usually think about a comment the editor (Glen Latham, I think) of the Cast Bullet Association's "The Fouling Shot" made in an article or editorial twenty-five or so years ago.

I don't recall the exact words, but someone, perhaps the author, might. The editor mentioned that the softest bullet fired at the highest velocity that doesn't cause leading will usually be the most accurate (probably for that bullet in that rifle). I hope I didn't alter the meaning of the author's message with my poor memory, but I believe there is much truth in the statement. Using the largest diameter bullet that will permit a loaded cartridge to chamber without difficulty may be another important factor.

Formulas and computer programs likely have a place in the way of rough guidance or shortcutting some labor, but physically trying something still has merit.

[sqlbullet]

The question has been answered. No.

A shower thought or two as I read this thread.

Bearing surface, alloy, lube, bore condition and heat treatment all will affect the actual final maximum pressure.

Even changing from one jacketed bullet to another invokes the "reduce 10% and work back up" instruction that all to many of us ignore.

[John Boy]

extensive experimentation has revealed the empirical correlation of 3 x 480 x Brinell Hardness Number (BHN) (or more simply, 1440 x BHN) as an estimate of the minimum peak pressure required for bullet obturation
http://www.lasc.us/FryxellCBAlloyObturation.htm

[Larry Gibson]

What relevance does that formula have to the OPs question?

[sutherpride59]

Lol because that formula was the main reason I was asking in the first place lol.

[sutherpride59]

I don’t see much point to the formula if there is no way to get an idea of what your pressure is going to be with a load.

[Rcmaveric]

You can roughly calculate with Richard Lee's formula from his reloading manual. Its simple math as you as adjust the load max of powder by 1 grain you muliply the max load pressure by what ever it says like example .983. You can make a table for it. The down side is that if the load is for jacket bullets it will have a different pressure for cast because of the less resistance of the lead, but if you seat into the lands you going to cause a pressure spike and the pressure can be much high. I have done it and found loads for BLC-2 and 4064. Now if richard lees load data is for a cast bullet it will get you closer in the ball park. So if you are using jacketed load data for cast then the estimation is a loose stretch. Aslong as you start low and work up while keeping in the guidance of reduction limit it is safe.

QL is a better way of estimating pressures and velocity. I am normaly 25 fps fast on my chrono than what QL tells me.

However the PSI limits is not hard set rule of thumb. If your bullet fits it can be shot softer.

While i do beleive that the lead has pressure and force limits. I dont think the pressures we estimate are the limit. There is more at play than simply PSI and torque. I still start light and will go over what i estimated. You never know what might work and worst thing thay will happen is i clean some leading out of my gun. I let the bullet tell me how it wants to be shot.

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[Rcmaveric]

Slap a gas check on a bullet and you just changed its pressure limit also. Those lead pressure estimation dont take into account a gas check. Still can be used though.

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[Larry Gibson]

Slap a gas check on a bullet and you just changed its pressure limit also. Those lead pressure estimation dont take into account a gas check. Still can be used though.

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Nor does the formula take into account the alloy used. The formula is based on the pressure needed to obturate lead.

Many of us shoot cast bullets well above the "failure" level that formula prescribes.

[Rcmaveric]

Nor does the formula take into account the alloy used. The formula is based on the pressure needed to obturate lead.

Many of us shoot cast bullets well above the "failure" level that formula prescribes.Agreed. Some times, with the way I think, I need a starting point though. Thats a good safe starting point to work up a load.

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[Larry Gibson]

Note also the Fryxell/Lee formula is intended to determine the psi at which "obturation" begins. It does not determine the psi of any "load". Fryxell was also referencing bullets in revolvers needing to obturate to seal the cylinder throats. The formula does not reference calculation of a loads psi.....hence my questioning the relevance.

BTW; the formula says my 30 XCB cast of #2 alloy (WQd) with a BHN OF 22 should obturate at 31,680 psi.....yet at 2900 fps pushed at a measured psi of 49-50,000 psi recovered bullets and excellent accuracy show no sign of obturation.......or alloy failure.

[sutherpride59]

Exactly how do you tell if obturation has occcured in a recovered bullet? I just thought it was a concept and the best way to tell is at what bhn your bullets get the best accuracy? It took me a while with my 45!but I found my most accurate bhn was 11 with my uspsa loads. I just figured this was when the obturation was occurring.

[sqlbullet]

Telling what occurred in the barrel is really challenging unless you have a budget for equipment that dwarfs the GDP of many nations.

Which is why we ultimately rely on accuracy to tell us what is going on. It really is the only thing that matters in our little hobby.

And, while elastic and plastic deformation ranges and pressure can inform why a given load in a given gun may or may not be accurate, they don't matter much given the relatively simple formula that works 99% of the time.

Make sure you bullets fit. Slug that bore and size .0005"-.001" over the measured value.

Start softer than the internet will tell you. Bullet too hard causes more guys issues than bullet too soft. And, leading from soft lead is easier to get out IMHO.

Reduce 10% and work up. This is the part that starts to really feel like work if you actually do it. Five shots isn't going to tell you. Fifty starts to give you a clue. And that gets worse as the gun gets more fancy.

Finally, detailed records. We have all been there. Got the range, fired ten 5 shot groups that grouped .0000001" even taken together. Ammo ran perfectly in our gun. There was nothing downrange too small for us to hit with that bullet and load. Come home on cloud-9 that we have the magic recipe. Only to find that it was mystery alloy #6, no idea the pot temp, quenched or not or final hardness of the bullets. Can't remember how I sized them or which lube I put in them. And what primer was it again?

I love a good scholarly article as much as the next guy...Usually more in most gun groups. But at the end of the day, the steps to finding a good load don't require us to actually know the PSI of our load.

[fredj338]

Without specific load data is there anyway to calculate the PSI generated in a cast load based off of copper jacketed data? I know this isn’t most important thing in the world But it would be nice to be able to guesstimate how much psi is going to be on my cast bullet based off a jacketed data.

In a word, no. Generally a lead bullet at the same powder charge as jacketed will have a bit higher pressures IMO.

[fredj338]

Would Quick Load provide any information on pressures?

Too many bullet variables I suspect.

[Shiloh]

Won't it vary per different alloy??

Shiloh

[sutherpride59]

Won't it vary per different alloy??

Shiloh


I’m sure it would but I just their might be a formula that took all that into account. Maybe I should just start emailing the powder companies if I’m truly curious about it.

[Rcmaveric]

Min and Max psi would be calculated from a bullets BHN. So yes and no. Alloy content doesn't really matter but the actually BHN does. The math does not take into account how antimony aides in obturation and how tin resists obturation. But these numbers and math are all therotical.

[trapper9260]

I go with Larry Gibson stated. too many things will change from what one things.So there is really no way with out have some other information. It is not only the powder and alloy that is used but also the gun that it is used in also.Also the twist of the rifle.

[Larry Gibson]

Min and Max psi would be calculated from a bullets BHN. So yes and no. Alloy content doesn't really matter but the actually BHN does. The math does not take into account how antimony aides in obturation and how tin resists obturation. But these numbers and math are all therotical.

Isn't that a little backwards?

[sutherpride59]

Yup you got those two backwards bud lol. Antimony is brittle tin is very flexible.

[Rcmaveric]

Yup you got those two backwards bud lol. Antimony is brittle tin is very flexible.

That's the characteristics it has on target. Under pressure it acts a bit different. That's why swaged bullets have antimony and no tin. Antimony is good for the lead under pressure. The long chains break and help the solid lead flow under pressure. Tin resist that extrusion under pressure and is why it is not in jacketed bullets. Maybe it makes a difference when fire, maybe it doesn't. Its all theory and speculation.