Using a digital thermometer & thermocouple probe placed in the bullet cavity & with the mould setting on a hotplate, I’ve determined that the ideal starting temperature for my BACO 409400M4 .40 caliber single cavity cast iron mould should be around 575 degrees F. At that temp the 1st bullet that drops out of the mould is within 0.5gr of all the rest. At 500 degrees it requires 4 or 5 bullets to bring the mould up to the correct temperature, at 450 degrees 10 to 15 bullets are required. Of course a cold mould would require more.

BTW, I’m casting the 400gr bullet at 765 degrees with 16:1 alloy & using a PID controller. I do not monitor the mould temp while casting.

Wayne

Guys,

I’m revising the hotplate mould temperature I posted earlier. Due to a response from an experienced caster that monitors his mould temp, I just checked the calibration of my digital thermometer setup. Apparently the thermocouple probe I was using is bad. After switching to another probe and checking the calibration, the correct hotplate mould temp is around 465 degrees F. Interesting, it’s been my experience that when a thermocouple fails it typically reads less than the actual temp rather than more.

My technique was to over-heat the mould then cast until the bullets lost their frosty appearance, at which point the mould temp was measured by inserting the probe into the bullet cavity. From experience I know that as soon as the bullets lose their frosty appearance the weight is within +/- 0.5gr of their average weight.

See the photo below for my initial setup. You'll note the digital thermometer reads 465.0 degrees and the PID in the background reads the casting alloy temp of 766 degrees (1 degree over the setting of 765 degrees).

Wayne

Mac, could you elaborate a bit on the device you have your pot plugged into? I am ignorant of it. Am I suspecting correctly the device maintains melt temp? The stat on my ancient Lyman has been dead for a decade or two and I monitor the melt temp with a lead thermometer then regulate it by unplugging and plugging in the furnace. It works but sometimes I get busy casting and forget. Needless to say what happens to the melt temp.

It's called a PID Controller. It controls the pot temp to within a few degrees from a predetermined setting. Here's an article on the subject that I wrote some time ago & recently updated.
http://www.texas-mac.com/Casting_with_a_PID_Controller.html

Wayne

That was certainly interesting and a great help, thank you!. Evidently over 40 years of casting bullets I've stumbled on to a technique/method that works for me. Once everything is up to temp my bullets will hold within less than a grain weight so long as I keep an eye on the thermometer. Still....I'm getting older and lazier and would rather not have to watch the thermometer so close. Is there a unit available "over the counter" or are they strictly on a custom basis?

Interesting. Only casting I have done to date (in bullets) is .50 bullets for my muzzleloader. And I was taught to float the mold on the hot lead to keep it at proper temp.

I can't help you there although I have heard that someone on the Cast Boolits forum does sell PID controllers.

Wayne