To heat-treat bullets in the oven? Does it actually take an hour to bring the bullets up to temp? Or, is something else going on that takes time?
The reason I am asking, is that a thought ocurred to me. If you heat-treat to the max temp, but for a shorter time, (say, 30 min, as opposed to 1 hr.) would this harden the exterior of a bullet, and leave the core a bit softer? Wouldn't it be somewhat like case-hardening. This seems as if it might be a good thing. you would have the benefits of a hard exterior, and the greater ductility of the softer core.
Or does it just not work like that? Inquiring minds (or simple ones, in my case)want to know!.........Thanks.

Bug, like silver and gold and unlike iron, heat goes through lead like gang busters. So, this concept makes one think that for all practical purposes the temp in the middle of a boolit is very close to the temp on the outside of the boolit. We also know that water cooling in A/C work is much more potent than air cooling, and this is why geothermal A/C systems work good. It stands to reason that water cooling will work with boolits too. In reality, it is the transient response of the lead's heat gradient is the mechanism which makes the boolit go hard. The sudden change in temp is the name of the game in lead alloy hardening. The hour business is just about required because we want all the activity within the boolit to be as constant and quiet as possible when the dunking occurs. This optimizes the transient effects. ... felix

Hi Ricochet! That was one of the shortest and clearest explainations of quenching I have ever heard! "So Cool!", as the kids say.





Oh, my point! I heat treat right out of an automated casting machine.... Exact adjustable timers control the pour, the wait before the sprue is cut, and the wait when the blocks are open for cooling. You can make WW harder than linotype- this I know. Dale

Here's what's happening: When the alloy cools down, a bit below the solidification temperature antimony (and some other alloy metals as well) becomes incompatible with the crystalline structure of lead. Above this temperature it's in a uniform "solid solution." When the alloy cools slowly, the supersaturated antimony is pretty mobile within the lead crystal lattice, and will migrate to form relatively large crystals, the lowest energy state for it. This results in a soft alloy, as the lead's malleability is due to the easy slippage of the atomic planes in the lead crystals and the relatively few and large crystals of precipitated antimony don't do much to disturb this. When you suddenly quench the "solid solution," it's trapped in that form at a temperature way below where the antimony can "dissolve" in the lead. For a short while it continues in this state, but it's unstable. The antimony atoms will clump together and form separate crystals in a lead matrix as before, but because the antimony atoms can't move so readily in the cold lead, they migrate short distances and form many very tiny crystals. These pin together the slipping atomic planes of the lead, making the alloy much harder. Back to the original question: When you start heat treating boolits that have been annealed, they contain the relatively large and few antimony crystals. You must first heat them to a temperature above that at which the antimony can exist as a "solid solution," then maintain it long enough for those crystals to dissolve and for the antimony to diffuse more or less evenly through the matrix, then you can quench it. If you're casting and drop the bullets from the mould into the water before the antimony begins precipitating, you get optimum hardness without the wait. The problem is in judging when the temperature's just right, and you have more control of that with the oven treatment. (If you move fast from the oven to the water.)

Ricochet, Kudos for your explanation of metallurgy! For Bug & Dale, you can heat-treat for 50 mins. at max. temp. for your alloy (WW + 1% Sn I assume) and exceed the hardness of linotype...in theory. I.e., you can surpass lino's hardness IF you first size and then oven heat-treat. However, if you water-drop and then size your CB's you will have drastically softened the outer layer of the
bullet according to metallurgist Dennis Marshall. In other words, there really IS a difference between theory and practice in this instance. ...Maven

Thanks, guys!

Yeah, lead alloys are kind of opposite to other things we're used to (like brass) in work softening rather than hardening.

I've been skipping a lot of this work myself, by cutting off the sprues as soon as they're solid enough to and dropping the bullet from the mould into water and shooting the boolits as cast, without sizing.

Very good explanation, my hats off to you. I too am lazy and water drop and shoot without sizing. I get excellent results so I won't bother with the oven method. I have never figured out how to keep the soft boolits from getting damaged on the trip into the water. I can't picture a pan full of boolits getting poured into a bucket. (least of all in the kitchen. A 500 degree boolit on the floor is not good.)

I have trouble with the still-soft bullets getting dinged up in the drop, too. Putting something soft in the bottom of the bucket prevents that only until the bullets start piling up, then the new ones land on previously dropped, hard bullets. That's where the dings come in. I suppose putting a "ramp" of something soft and springy enough not to dent them under the surface of the water, that would impede their progress and then let them roll down into the pile, would alleviate the problem. Just thought of it, though, haven't tried it.