How to figure out bhn

[PALADIN45]

I have a question. MO Bullet says to compute BHN this way CUPS/1279.8=BHN.

20,000 CUP/1279.8=15.62 BHN give or take.

Here's another one, To compute bullet hardness, divide the chamber pressure by 1400 if rated in psi or 1440 if rated in CUP.

20,000CUP/1440=13.8 BHN give or take.

Which one is it?

My Speer reloading manual doesn't even give pressures for a load. I can't even compute it.

Hodgdon does, for a 45 Auto LSWC with 4.8 Grains of Titegroup I would be at about 13,400 CUP 877 FPS.

13,400 CUP/WHAT?

Hodgdon gives me a Primer, Powder, Velocity, and Pressure. Speer gives me a Primer, Powder, and velocity. No pressures for those loads.

I need pressures to compute BHN.

It's a 2 part Question, any gouge you guys have would be appreciated.

[geargnasher]

I dunno about the 1279.8, I've always gone with 1422 since it is the conversion factor from Kpa to PSI. Keep in mind that this formula is a guideline, not gospel! I can tell you for certain that 10 BHN alloy will handle 13K CUP (not psi) in a .45 ACP all day long without a trace of leading if you use a decent lube and the boolit fits the barrel correctly.

Not sure what the CUP/bhn conversion really is, but if you troll around you can get some loading data in PSI so you don't have to convert.

Gear

[btroj]

Can say I have anything to add. Don't worry about the bhn anyway. Don't have a hardness tester. I try to keep it simple.I cast, I load, I shoot. No more than the minimum
I wonder if some of the new guys are over thinking things. Some of these types of topics are great for concern in specific situations but for general shooting they are not necessary.
Just my 2 cents.

[geargnasher]

[snip]I cast, I load, I shoot. No more than the minimum.

And that, good sir, is probably the best advice anyone will post on this thread unless the subject changes to pushing the envelope of performance and accuracy in a smallbore rifle.

Gear

[HangFireW8]

I have a question. MO Bullet says to compute BHN this way CUPS/1279.8=BHN.

20,000 CUP/1279.8=15.62 BHN give or take.

Here's another one, To compute bullet hardness, divide the chamber pressure by 1400 if rated in psi or 1440 if rated in CUP.

20,000CUP/1440=13.8 BHN give or take.

Which one is it?


I don't have those sources handy, but I suspect one is calculating the exact deformation strength of the lead, and the other is calculating the 90% value of the same, which is the Lee & Veral "rule" for ideal hardness for a given pressure load.

I put the word [I]rule/I] in quotes because it can be violated without consequence in many cases.

-HF

[dromia]

Welcome to Cast Boolits Paladin45. :drinks:

See you've got plenty of sound advice already. :-D

[runfiverun]

i ain't so good at math so i take the bhn and times it by 1400 to get the pressure that should be at bout 90% of the alloys compression strength. [which is usually about half what i need the pressure to be]
but my memory ain't so good and i forget to write it down.
so i just use ww's and soft 75/25 in the revolvers/auto's and leverguns with plain based boolits.
and the same alloy waterdropped with gas checks in the rifles and shoot for accuracy.
or i use my 4/6 alloy if things are going faster than 1900 fps or if the mold isn't pouring quite large enough. sometimes waterdropped ,sometimes not.