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 is 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

Interesting, Wayne. The only BACO mould I have is the 600-grain for .50-70, and I am a sloppy caster using whatever I can find -- although I keep some 20:1 for serious work -- and cheap Lee Production
Pots. Someday maybe I will get serious and cast some really consistent boolits like you do.

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

I used to pre-heat my Hensley & Gibbs moulds on the griddle plate of the kitchen cooker on which the housekeeper made dropped scones. The bullets were full and dropped cleanly from the very first sprue of six that were cast each session. I also used an RCBS Pro-Melt. But what is the feedback, please, on the Lyman Mag-25?

I pre-heat moulds by floating the blocks on the molten lead. This gives a hardened blob that will fall away cleanly once it gets hot enough. A couple fills later you're casting perfect bullets. Might even be the first one although I seldom even look at the first few.

quote:

Originally posted by Dogleg:
I pre-heat moulds by floating the blocks on the molten lead. This gives a hardened blob that will fall away cleanly once it gets hot enough. A couple fills later you're casting perfect bullets. Might even be the first one although I seldom even look at the first few.

I'll try that, thanks.
Previously I just left the mould sitting on the top edge of the pot as it heated up.
Henceforth it is going to float in the center of the pot.

Rip ...

I use a hot plate. I bent a piece of sheet metal to hold the mold a bit off of direct contact with the heater element and made a small box of sheet metal with pop rivets to go over the mold to hold heat around the block. A barbecue thermometer in the box lets me monitor the temp. I start the block heating as I start the melt. Everything is ready to cast about the same time. I like the block temp around 400 to 450* F.

I believe this produces much less stress on the blocks and gives a much more even heat soaking than just setting the block directly on the coils or floating in the lead.

I just set the mould and handles on the top of the RCBS Pro melt furnace.
The sprue plate lays on the top of the bar that connects the spigot.
This keeps the mould out of the lead and off the top of the furnace and warms things up nicely.

Cast for an hour and half yesterday, got 8 pounds of good 30 caliber x 200 gr bullets and only had about 30 culls

Just my 2 cents

JW

I'm not landing any of my bullets on the moon, so I don't get as technical as you folks.