I don't know about zinc, I've tried to get the stuff to mix and pour but can't do it. It pops up to the top of the pot looking like gray cottage cheese. I always set my PID controller to 800 degrees but rarely if ever achieve it but do run in the 780's. Being cheap I'd like to get the zinc to mix in to get more bullets for plinking purposes - too hard to do what I want for hunting. I just can't believe what we are seeing here is zinc. It looks like the metal was cooling too fast in layers before the cavities could fill out and that was probably a cold mold issue I'm betting. Some people are using hot plates for pre-heating molds and will tell you that dipping a mold in molten metal could warp it. They may be right but I started casting as a broke college kid so cheap was the way I operated and dipping the mold in the pot is free whereas a hot plate costs $'s.
I DO like to set the mold on top of the pot for maybe a couple minutes some times before dipping it into the metal so it's not so drastic a temp shock.
Heck I had it full blast as hot as it would go. Lol
The classic sign of zinc contamination is that the mold won't fill out.
Pure lead melts at 621.5 F.
Zinc melts at 787.2 F.
There's ways to test for Zinc using muriatic acid and to watch closely for any kind of bubbling reaction. or use a thermometer and remove the zinc before casting.
Pure lead will not react to acid.
Zinc bullets will weigh less than pure lead bullets. and will be harder.
The higher the percentage of zinc, the worse that the bullets will come out.
The fact that the OP needed to blast his heat in order to cast is an indication that too much zinc was in the mix.
The photos of the bullets shows it since they couldn't hold their shape.
Some folks have said that any more than 2% zinc can ruin the alloy and those bullets look pretty bad.
I wonder what they measure and how hard they will be to load.
I've got a chance at a boat keel, or at least part of one. Haven't seen it yet, but the seller guesses half a ton and says he's been told it's pure lead. I rather doubt it's pure lead, my only concern is Zinc in the mix. I've read about using muriatic acid to test for zinc. How reliable is...
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