Is there a formula to equate/calculate diameter change with alloy change?

[Scheyville Shootist]

Hi All,

I have recently started casting heavy boolits in 20:1 for use in BPCR matches. My Lyman mold 457125 is dropping these at .461 - way over what I need (.459) for my Pedersoli Sharps. I buy my alloy ready made from a foundry in Queensland and it is very consistent.

Is there a formula that shows the relationship between changes in alloy and casting diameter? I have cast Lyman #2 to use in my pistols for many years and it always drops close to the nominated diameter, so I assume that changing the alloy to say 15:1 would reduce the diameter in the Lyman 457125.

Is this correct? Any help appreciated, getting accuracy for this Long Range BP shooting is a lot harder than loading for cowboy action!

Regards from Down-under.

Scheyville

[jsizemore]

The higher the Pb content the smaller the boolit diameter. The hotter your alloy casting temp the smaller your boolit diameter. Go to the www.lasc.us website and read up on boolit shrinkage with different alloy. Go to the Cast Bullet Notes page and about half way down will be shikage percentages.

[Scheyville Shootist]

Thanks, just what I needed - I knew someone here would know where it was, my internet search skills are sadly lacking.

[jsizemore]

Lots of good stuff on there.

[badgeredd]

Hi All,

I have recently started casting heavy boolits in 20:1 for use in BPCR matches. My Lyman mold 457125 is dropping these at .461 - way over what I need (.459) for my Pedersoli Sharps. I buy my alloy ready made from a foundry in Queensland and it is very consistent.

Is there a formula that shows the relationship between changes in alloy and casting diameter? I have cast Lyman #2 to use in my pistols for many years and it always drops close to the nominated diameter, so I assume that changing the alloy to say 15:1 would reduce the diameter in the Lyman 457125.

Is this correct? Any help appreciated, getting accuracy for this Long Range BP shooting is a lot harder than loading for cowboy action!

Regards from Down-under.

Scheyville

You'll likely get a lot closer to you target diameter with 40:1 alloy. The less tin you use the smaller the bullet diameter. I have used tin and tin based babbit to increase my bullet diameter in a couple cases.

Edd