Bullet Hardness and Pressure

[gzig5]

I'm going to start playing with my 460 Rowland kit. I have some RCBS 45-200 that seem to fit the longer case while keeping OAL in check. I've cast some @11 bhn or so for my 45acp and powder coated them. I'm not going to load them nuclear, probably 1200fps or so as I ease into it. Loaded some behind 10, 10.5, and 11 gr of Longshot. Is that hardness going to hold up at ~25-30k PSI or will I need to use a harder alloy? I know, one way to find out... Just going through paper and plinking for now. I'll probably use a 230-250 gr bullet on deer. Hoping to get some insight from those that have run the Rowland, 45 Super or other higher pressure rounds like this with cast bullets.

[mehavey]

My personal experience is that the 1,420psi/BN factor can be multiplied
by ~1.5 --> BHN of 11 --> 23,000 or so before getting into real trouble.

[onelight]

Lee has a chart of what they recommend in the instructions of the hardness tester.
https://leeprecision.com/files/instruct/LT2140.pdf

[guy_with_boolits]

Lee has a chart of what they recommend in the instructions of the hardness tester.
https://leeprecision.com/files/instruct/LT2140.pdf

That chart seems to suggest much lower pressures for 7BHN range scrap than some people seem to have good results with in 45 ACP. 9BHN at 11,000 psi??? How is anyone loading hollow points like that?

[dtknowles]

I don't think the Lee chart of pressures is of any use. Does not seem to match common successful usage.

Keith said that .44 magnum bullets should be at least 16:1 which is a BHN of 11. The .44 Mag. is a 30K psi plus round. The Lee chart would make you think you need linotype but you don't. Bullets stripping is more a matter of torque than pressure. BHN of 11 might be a little weak but you don't need to bump is up much 12 or 13 would be more than enough.

Tim

[P Flados]

For me, Powder Coat has completely changed the game for high pressure cast bullet loads.

For a lot of my casting I use range lead that typically runs close to 10 BHN. The load below was a while back and the bullet may have been slightly harder. Probably somewhere between 10 BHN and 12.5 BHN.

With my powder coated custom 200 gr NLGs and WC 680, my 357AR Max seemed to want to shoot better the hotter I was willing to go. One batch did real good for accuracy (2 MOA at 200 yards) and velocity (2050 fps), but pierced one primer in a batch of 5 (see photo). The above was not an isolated case, there were quite a few batches that I had to back down on due to getting pierced primers. Accuracy in this gun never "went south" as loads got hotter.

Later after getting Quickload, I ran the numbers and the calculated pressure for the load below was just over 60,000 psi.

[mehavey]

That chart seems to suggest much lower pressures
See http://castboolits.gunloads.com/showthread.php?306943-quot-optimum-quot-Brinell-hardness-amp-Missouri-Bullets-WARNING-MATH-!&p=4409805&viewfull=1#post4409805
Empirically, I've found 1.3-1.5X to be the practical multiplier to the classical 1,420psi/BN factor.


How is anyone loading hollow points like that?
And like P_Flados, I've found PC'g to literally double the higher end of that factor.
http://castboolits.gunloads.com/showthread.php?409893-Pure-Lead-amp-PC&p=5001471&viewfull=1#post5001471






In the end, it's all magic .... So don't cast a thousand of anything until you've
cast a dozen of something... and tested in your gun against your expectations

[Larry Gibson]

The pressure to velocity chart in both the Lee manual and the Lasex writings/site use a constant in the equation that is for the tensile strength of lead. With a binary, ternary or quadranary alloy the tensile strength of the alloy is different. Hence, without the correct constant the computed result is meaningless. For example; I use a #2 alloy in my 30 XCB bullets and push them to 2900+ fps at an actual, not guestimated or computed, 50,000+ psi (measured with an Oehler M43 in the firearm). Using the formula tells me the alloy should fail well below that pressure. The alloy does not fail as I have shot moa accuracy with 10 shot groups to 600 yards with that alloyed bullet at 50,000+ psi.

The use of that formula was an attempt to "prove" why accuracy failed (because the bullet "failed") at a certain velocity level, most notably in rifles such as the 30-06, etc. What was not understood by the developers of the formula was the reason for failure (loss of accuracy) was not the pressure but was the RPM.

The formula does work fairly well if pure or a mild binary alloy (lead/tin)is used is used.

[mehavey]

#2 alloy in my 30 XCB bullets and push them to 2900+ fps
at an actual, not guestimated or computed, 50,000+ psi
Plain-based, or gas-checked Larry ?

[Larry Gibson]

GC'd of course. I know better than to claim such with a PB'd cast bullet.

However, I have also pushed PB'd 44 bullets to 45,000 psi [M94] w/o any evidence of alloy failure when the formula said it should have failed well below that pressure level.