Shrinkage

[armednfree]

Flipping through From Ingot to Target: A Cast Bullet Guide for Handgunners I find a statement that a pure lead bullet will shrink 1.13%. My Lee C452-300RF cast from range scrap and aged a year (or more) is .453. So if I use that as a base:

.453x.0113= .005

.453-.005= .448

I find that hard to believe.

[redhawk0]

The sentence directly before it is the context of that statement. Its not over time...is of a newly HOT cast boolit.

"Antimony also helps to reduce shrinkage as the alloy cools."

[EDIT] Many molds are designed with some shrinkage built in. That's why we talk about the diameter of what our molds drop....not the "actual" diameter of the mold cavity.

redhawk

[armednfree]

I know it doesn't change after it cools, but what can I expect that mold to drop? These are being paper patched to shoot in a 45-70.

[redhawk0]

Every mold is slightly different. You will need to cast and measure. If you're dropping at .453" then you should be right there for paper patching.

redhawk

[bdicki]

[marek313]

When I was clicking on this thread i wondered how many cold shower / pool comments there will be here

[fredj338]

Every mold is slightly different. You will need to cast and measure. If you're dropping at .453" then you should be right there for paper patching.

redhawk

Especially molds cut on cherries. A 6cav mold is not likely to have any of the 6 match.

[fredj338]

I know it doesn't change after it cools, but what can I expect that mold to drop? These are being paper patched to shoot in a 45-70.

Too many variables; casting temp, alloy, exact mold cavity dims, only way to know is start casting.

[GregLaROCHE]

I’ve found the hotter the alloy, the lighter the boolit will be. I suppose this comes from the alloy contracting when it cools. I assume the diameter will decrease too. Different alloys probably shrink differently also.

Best way is to cast and measure. I don’t believe time after they are cool makes much of a difference. It does on hardness though.

[fredj338]

I’ve found the hotter the alloy, the lighter the boolit will be. I suppose this comes from the alloy contracting when it cools. I assume the diameter will decrease too. Different alloys probably shrink differently also.

Best way is to cast and measure. I don’t believe time after they are cool makes much of a difference. It does on hardness though.

That is the shrinkage playing out. Why I try to keep my casting around 700deg.

[armednfree]

If pure lead is difficult to fill out and that is why a bit of tin is added I have an option. I have some 92-8 pewter which would give me something like 1-44 mix (off the top of my head) and only .0016 Antimony when mixed with 50 pounds. I have to think the difference in BHN between that and pure lead makes little difference.

Of course that is not something I'm going to do off the rip. If I get a high reject problem then I would try that.