Heres a thought

[beanflip]

Would freezing cast boolits help out with curing, lubing or sizing?

[44man]

Not to any given extent. Best to size and lube soon after casting and let them harden more. I don't though and never notice much difference in groups.
I think a lot of stuff is way overblown anyway. Size and fit is more important then a small difference in alloy or hardness. I believe the type of lube is more important then the small lead differences.

[Scrounger]

Felix, if you're reading this, many years ago I read an article about cold-treating tools and things to get the same benefits as heat-treating. Someone finally figured out that the process had applications in the gun field and started a business freezing barrels. Now I wonder if it's possible to cold-treat lead bullets to make them harder? Might be easier to work with than heat treating...

[felix]

This is true, Art. All Japanese tools were cooled before warehousing. I have no idea if this practice is continued because of energy costs. For a lifetime tool, maybe the cost benefit ratio would be low enough for sales. But, not for a boolit that will be made and shot within a day or two. ... felix

[Ricochet]

Hardening of solution-treated lead alloys occurs from recrystallization, which occurs more slowly as the temperature drops. Takes a week or two to see peak hardness after quench hardening at room temperature. If you want to delay this process, freeze the boolits. Heating them to a temp around 200F for an hour or two speeds the hardening, in case you want to shoot them a few hours after casting and quenching. Won't see any hardening benefit from cryo treatment, though.

[Trez Hensley]

The barrel freezing is done with cryogenics. Very cold. Are you going to use liquid Nitrogen in this endeavor? Maybe dry ice? I'm not sure if extreme cold is necessary to effect the molecular structure but it may be in order to see any big change in hardness. Cryogenics, from what I've read hold this frigid temp. for a specified soak time and "tempering" time just like oven heat treating. Just a thought about this FWIW.

Maybe Ricochet could enlighten us about the details.

Edit--I was typing this while ricochet was posting, as when I got it done I saw his post...

[jonk]

I tried freezing some to get the lube- LLA that was still tacky- to harden up more. Then I tried seating the gas checks with a Lee push through die. Much harder to do. But I think that hardness benefit was only realized so long as the slugs were still freezing cold. Not that it makes much sense how maybe 50 degrees difference could matter but it seemed to.

[44man]

Well, you could do what I tried the other day! [smilie=1: I grabbed the .432 Lee die instead of the .452 and tried to force a .453 boolit into it. Had to scratch my head, pour a stiff one and learn to read. :drinks:

[runfiverun]

i think the super cold helps to line up the molecules in the metal...
you might be able to get a more consistent alloy mix if you freeze them?????
also is not water-dropping a form of freezing??
or is that just tempering...

[Ricochet]

What I've read about cryogenic treatment of steel (about which I'm pretty ignorant) is that it works largely by converting residual austenite in hardened and tempered steel into martensite. Completes the hardening from quenching, which approaches but doesn't quite reach completion on cooling to room temperature.

Lead alloys work differently than steel. The hardening mechanisms are different. Most steels harden when the austenite converts to martensite on quenching, essentially instantaneously. The lead alloys that harden with quenching don't get really hard right after quenching (often they're close to the hardness of pure lead immediately after), but harden over a period of time aging at room temperature, as alloying elements that are soluble in solid lead at the pre-quench temperature but not at room temperature gradually precipitate out. That'll still happen if it's very cold, but happens more slowly because the diffusion of atoms through the matrix to form crystals is slowed down. Elevate the temperature to 200F or so, and the age hardening happens much faster. Elevate it somewhat higher, and the atoms can freely move to form larger crystals that don't harden the alloy nearly as much as the more numerous, smaller ones that form at lower temperature. That's why annealing works to soften bullets. Heat 'em up to a temperature that puts the alloying elements in solution, then very gradually cool 'em down. They'll be softer than if air cooled from the mould.