When my supply(s) of lino looked to be drying up, I contacted a friend who is part owner of a small company that casts pistol bullets and bought 100+ lbs. of the alloy he uses. It comes from a local foundry, and the stuff I got was straight from the foundry, with their name cast right into the bars, and with the alloy composition (91-7-2) stamped on every bar. I figured I'd try it for rifle bullets as is, and if they weren't hard enough, with 7% antimony content I could always heat treat the bullets and get them up to lino hardness or better. Some time ago, I acquired a small toaster oven for just that purpose.
The other day I cast a bunch of Lyman 311679 bullets using the 91-7-2 alloy, and decided to go ahead and do a trial heat treating run just to see what would happen.I selected 2 bullets, both from the same cavity, with no visible flaws and within 0.3 gr. weight. I ran the toaster oven, set at 450 degrees, for about a half hour with my Lyman casting thermometer in it, checking the thermometer through the window to make sure the temperature didn't fluctuate too wildly. As near as I could tell, it held at 440 degrees within +/- less than ten degrees. I measured the length of the two bullets and wrote the measurement on each bullet with a “sharpie” pen. Then I cooked one bullet at 440 for one hour (with an aluminum tray under it and a sheet of aluminum foil over it), opened the toaster oven door and immediately quenched the bullet in tap water. It made a very gratifying hiss when it hit the water.
I waited about 24 hours and then put the heat treated bullet and its un-heat treated companion base to base and squeezed them in a vise until I could see a visible shortening in the two bullets, and measured them again.
The heat treated bullet had shortened 0.049". The as-cast bullet had shortened only 0.042"! Just backward!
Somebody give me a hand here. What did I do wrong?