Mould Temperature

[FISH4BUGS]

I have a Lyman 358156 158 gr swc gc 4 cavity mould that I am casting THOUSANDS of bullets to size and lube in the Star. My goal is to get about 5000 casted up and size and lube them as needed, maybe 1000 at a time. Then I'll start the process over again when I run out. I may do this with each handgun caliber I cast for.
I am running the Pro20 at about 6.5 on the temp dial (I am going to get a lead thermometer soon) and using 5lbs ww to 1lb linotype alloy.
I have to cast probably 100 (or more) bullets before the mould comes up to temp and starts casting easily. During the first 100+ bullets the sprue has to be really hit hard to open. As the mould heats up, and the bullets start to show the slight frosting that tells me all is well, the sprue cutter gets easier and easier to cut. It sometimes is so easy to cut the sprue, I sometimes worry that the lead hasn't had time to fully harden and will smear, but so far so good. I watch the excess on the sprue cutter to get fully silvered and hard. I use the damp towel speed casting method to cool the mould. The first 100+ bullets are mostly usable, just wrinkled on the SWC nose (except for those that don't fill out quite fully).
I try to preheat the mould by placing it on top of the furnace. I wonder - could I preheat the mould on the gas stove at a low flame as the Pro 20 furnace is heating up? It seems that might help the casting get better bullets quicker, but I don't want to risk damaging the mould if that is a no no. I like this mould - it is a workhorse.
Any tips?

[BruceB]

For many years now, I have preheated the mould by placing it right on top of the molten alloy in the pot, with the entire bottom surface of the mould in contact with the alloy, or as much as 3/8" or so into the melt.

A 2-cavity Lee aluminum mould usually takes about fifteen seconds to be "hot enough". while I allow 25-30 seconds for a two-cavity iron mould and 45-60 seconds for a four-cavity iron mould. The best indicator of "hot enough" is that the alloy no longer is adhering and building up around the mould. There can be a very thin skin of alloy on the mould bottom, but no heavy clumps. The thin residue should wipe right off with a gloved hand.

Once the casting begins, the mould will arrive at its regular working temperature rather quickly.

In spite of many alarmists who throw up their hands and bleat about "mould warpage" I have never seen such an occurrence in ANY of the scores of moulds I've used in this manner over several decades.

[Beau Cassidy]

I generally set mine on the top edge of the pot when I turn it on. Most people seem to get their molds up to temp. faster than I have noticed. Still haven't figured that one out yet, though. As you have found, at least as far as I am concerned, it is hard to cast a decent bullet until the sprue temp has stabilized. Once it does, you are in a rhythm and can really roll. It probably takes me 30 minutes to get the mold AND sprue temp. stabilized on my 10 cavity mold.

Beau

[ben1025]

The best way I found to heat a mould is with a electric 800 watt hot plate.
Never no warpage even forgetting the mould on the hot plate for ten hours.
Aluminum or iron makes no difference. I even made 2 alloy bullets by melting lead in the nose of the mould on the hotplate and when melted use my bottom dump to fill the mould. I did learn quickly to rubber band the handles together.

[mooman76]

I cast on the stove and preheat my steel moulds by placing them next to the flame, not in the flame and that works well. It usually only takes a few csts to get up to speed!

[buck1]

I hang my mold on the rim of the pot , but OVER THE ALLOY.
4 or 5 cycles and I am cooking boolets!....Buck

[NVcurmudgeon]

Bugs, don't see why preheating your moulds with the gas stove won't work. I preheat mine by placing them near the edge of the Coleman stove flame. When the twelve lb. pot is melted, the mould is very close to casting temp.

[454PB]

I used to preheat steel moulds with a propane torch. I'd set the torch to it's lowest setting, lay the mould on a shelf, stack about 3 pounds of ingots on the handles, position the propane torch under the mould, and within two minutes it was up to casting temperature. I now have a 3000 watt electric heater in my shop which is in use while I cast in winter. I lay the mould on top of this convection heater while the lead melts in my Lee pot, and by the time I'm ready, so is the mould. I checked mould temperature with an infrared heat gun, and it was 240 degrees right off of the heater.

The other thing I've found is that my Lee lead pots cast best at 7 to 7.5, and I'm using an alloy nearly identical to yours. Just a week ago I was casting the 358156 in a two cavity Lyman mould, and the very first boolits from the mould were keepers.

[Dale53]

Even tho' I have been casting bullets for over fifty years (more like fifty five years) I am still learning. Just recently, due to a suggestion from a good friend who is also a custom mould maker, I started experimenting with placing my moulds on the surface of the molten metal. I ended up with about the same times that BruceB does (at least, close). I heat the two cavity Lee's up for 20-30 seconds, Iron moulds up to 2 minutes.

I even tried leaving an iron mould (large block one cavity schuetzen bullet) on for five minutes. It was definitely too much. The mould was the same temperature as the melt. When I opened the mould, the bullets were still liquid on the bottom. Further, small bits of alloy were clinging to the inside of the mould (on the bullet nose).

My ,mould making friend had told me that if I heated up the mould REALLY hot (like above) then used a fine grain brass brush it was a great way to thoroughly clean a mould. So-o-o, I tried it with the lead bits in the mould and they brushed right out.

I learned a couple of things, you can heat them TOO hot. You CAN clean an iron mould by doing so and then brushing it out with a fine grained brass brush. Finally, DO NOT DO THIS WITH AN ALUMINUM MOULD.

Aluminum is softer than brass and would, no doubt be damaged.

I will continue to pre-heat both moulds (iron and aluminum) by setting on top of the alloy (20-30 seconds for aluminum and up to 2 minutes on iron). I WILL NOT overheat them.

When pre-heated properly, by the second mould full you are running good.

Dale53

[felix]

I preheat molds by placing them on the cold melt, and turning on the pot, and go get a cup of coffee. By 15 minutes, the coffee is gone, and the lead is beginning to melt. Mold and HANDLES are perfectly hot (not the wood). ... felix

[44man]

There was a post somewhere for building a mould furnace out of an electrical box. The lid is hinged and a small thermometer installed. Make a cut out in the front side of the box for the handles to stick through. I made one and I put it on a cheap Wally World hot plate. Set for 500 degrees, I set the mould in when I turn on the pot and the first boolit will be perfect. The mould can be left in as long as it takes for the lead to reach temperature or all day if you want and it will never get too hot.
I even prop my second mould on top of the lid so it is in good contact and it comes very close to the right temperature too. A few passes across the sprue plate with my propane torch on the second mould and it is good to go. The mould gets hot but the sprue plate doesn't quite gather enough heat.
Of course you can pull the mould out of the oven and start casting with it and set the second mould in the furnace until completes heating.