If memory serves me correct, Marshall heat treats his labors of love, with a pizza oven he commandeered from a defunct pizzaria. I'm not sure of temperature or for how long. Trade secrete ! The bullets are then quickly water quenched. Hope this helps quench your thirst.
Go back and research Dennis Marshall's articles in American Rifleman in the 1980s, or get a copy of the RCBS cast bullet handbook.
For most alloys you can good results soaking bullets in a 450 degree F oven for 30 minutes and quenching in room temperature water. To calibrate your oven check the temperature at which distilled water begins to boil 212 degs. F, and that at which bullets of virgin linotype begin to sweat and slump over 473 degs. F. if you don't have a good laboratory grade thermometer.
At these lower temps is there any danger of lead coming off of the bullets & staying in the oven? I would think not but just got in trouble for running a carburator through the dishwasher the other day (hey, it's CLEAN!).
Simply get a used toaster oven at a tag sale and have at it. I use one all the time for heat treating. I hang an oven thermometer in it and run it to max at about 460 degrees with my alloy for about a half hour then dumping them into a 5 gallon pail of cool water. Over night set on a old towel to dry.
I get about 24-26 BHN with regular WW alloy.
If the bullets slump with your alloy, lower the temp until they don't.
When you are done, put the toaster oven away and don't lick the inside of it. I use the aluminum tray that came with it to set the bullets on in lots as big as 200 bullets.
You can then "draw" the bullets to whatever hardness you want through experimentation down to the original alloy hardness.
At these low temps you shouldn't get any vapor deposition of lead in the oven, but heat treating does give off a metallic smell and it sure keeps good will in the family if you clean the oven thoroughly after doing so, to keep other members of the family happy.
Here's what I've been wondering about for a long time but am too cheap to buy a hardness tester... I'd rather spend the money on moulds, powder, type metal, etc.:
Does heat treating (at about 450F) only case harden bullets or does it have the same effect as adding Sb to one's alloy. In other words, is a heat treated bullet cast of wheel weight metal and 25% type metal as strong (pressure resistant) as one cast from a 50/50 mixture of the same components and air cooled?
I realize this is a question that could take many hours of experimentation to answer honestly, or one could perhaps section a heat treated bullet and one hardened by the addition of antimony (but air cooled) to get an idea of how they would compare under pressure.
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