More Data Sources on Bullet Strength

[mtngun]

It's hard to find laboratory data on bullet strength and all too often casters rely on rules of thumb that are not good rules (I'm talking about you, 1422X forumula ! ).

What little data exists is usually for solders because apparently solder companies care about strength enough to actually test it. Here is some data found at this link:


And here is more solder data, if you don't mind converting the metric units to psi.

Let's take 10:1 alloy, with a tensile strength of 4400 psi and a BHN of 11.5. Linotype is about twice as hard so it's reasonable to assume that linotype would also be twice as strong -- 8800 psi. Heat treated wheelweight would be 3 times as hard so it's reasonable to assume that it would be 3 times as strong -- 13,200 psi. That's just a quick and dirty way to look at it, but it's a reasonable ballpark estimate. Lead is not made out of steel, folks.

[mtngun]

And yet another source, from Wilhelm Hofman's book "Lead and Lead Alloys." Unfortunately my notes lack the page number.

To convert the ultimate tensile strength (U.T.S) in kg/mm2 to PSI, multiply by 1422.

5 BHN ---> 2.5 kg/mm2 = 3600 psi
10 BHN ---> 3.8 kg/mm2 = 5404 psi
15 BHN --->5.9 kg/mm2 = 8390 psi

Note that the chart shows that BHN and Ultimate Tensile Strength with the units "kg/mm2." It's true that they have the same units, and some folks seem to jump to the conclusion "if they have the same units, they must be the same thing !" Sorry but it's more complicated than that. Tensile strength, yield strength, shear strength, compressive strength, and hardness all have the same units of force over area, yet they mean different things.

Another question that comes up is "well that's just the TENSILE strength? What about COMPRESSIVE strength?"

The answer is that it depends. If the material is brittle, like concrete, or like monotype, then the tensile strength will be less than the compressive strength.

But if the material is ductile, as most bullet alloys are, then it's safe to assume that the compressive strength is the same, or at least about the same, as the tensile strength. Ditto most ductile steels.

It's always better to measure the strength of a material rather than making assumptions and relying on rules of thumb, but in real life engineers make assumptions and rely on rules of thumb all the time. One of those rules of thumb is that you can usually predict the strength of a ductile metal based on its hardness, to the tune of 500 x BHN = the approximate strength in PSI.

[mtngun]

Another source, from pages 156 - 157 of Harold Vaughn's "Rifle Accuracy Facts":

According to engineering handbooks and the experimental stress tests that I ran in my hydraulic press on several samples, the core yield stress, or strength of the core can be determined by multiplying the BHN by 515.