Mould temp for big bullets has to be just right.
Couple days ago, I was running a batch of RCBS 45-300-FN for my Marlin M95.45/70.
Been a while since I ran any “heavy” bullets and I forgot the basic rules to make good ones. This is a double cavity mould and one cavity is a HP so it slowed things down a bit but I still had problems which I had previously found solutions to.
This mould, being an RCBS has generous sized mould blocks which also helps with the problems.
20 years ago, I was shooting some bigger calibers. .375 H & H, .40/65, .45/70, .458 Win Mag and a .458 X 2”. Several of my shooting partners were shooting like calibers.
I was turning out a lot of heavy bullets; some in the 545 grain range. A lot of these were using the old #457 series Lyman moulds with the old, small blocks.
Here in lies the problem. You can’t turn out many bullets with these before you run into problem. First, they cast wrinkled due to being cold, after this stage, it’s rounded bands as the moulds heat up, then for 2 or 3 rounds, it’s perfect bullets. Then, things begin to go downhill. First is frosting. Now, I don’t mind frosted bullets. Next is rounding bands and wings….rejects.This is due to the blocks being too hot.
Any time, you attempt to cast two bullets of 250 grains or larger, you will have these problems.
Then I said, John, you idiot, you’re casting too fast. Slow down the tempo and rejects go away and you get good bullets.
Why? The size of the mould blocks don’t dissipate heat fast enough and you have to have the heat with a bottom pour pot to insure proper filling of the big cavities with a sufficient flow.
About this time of big calibers, I ordered a .375 mould from Walt Melander at NEI. Talked with him on the phone and told him I wanted a meehanite double cavity. A spitzer in 300 grains and a RFN at 320 grains. He said, I can make it but don’t think it will cast. Was off the phone about 5 minutes and said, won’t make good bullets. Too much hot lead. Can I cast one cavity at a time. Yes, that will work. So I ordered it and when it came, Walt was right. Had to cast one cavity at a time.
This is one place that aluminum outshines iron moulds. It dissipates heat faster than iron does. Works well for large bullets but works against you with .22 calibers.
There are several ways to work around this problem.
The first is to time your casts. Maybe a bullet every 30 seconds. Even slower if necessary.
The second way is to use a cooling fan. I made one with a small cooling fan for a computer. Sitting a wet rag under this air flow and siting mould on it for a few seconds works to keep the temp of the mould down.
The third way is radical but works but we deemed it as impractical. We attached electrical equipment aluminum heat sinks to the mould attachment screws. It worked but made the mould clumsy to cast with due to added bulk.
The second method works the best for me./beagle
Couple days ago, I was running a batch of RCBS 45-300-FN for my Marlin M95.45/70.
Been a while since I ran any “heavy” bullets and I forgot the basic rules to make good ones. This is a double cavity mould and one cavity is a HP so it slowed things down a bit but I still had problems which I had previously found solutions to.
This mould, being an RCBS has generous sized mould blocks which also helps with the problems.
20 years ago, I was shooting some bigger calibers. .375 H & H, .40/65, .45/70, .458 Win Mag and a .458 X 2”. Several of my shooting partners were shooting like calibers.
I was turning out a lot of heavy bullets; some in the 545 grain range. A lot of these were using the old #457 series Lyman moulds with the old, small blocks.
Here in lies the problem. You can’t turn out many bullets with these before you run into problem. First, they cast wrinkled due to being cold, after this stage, it’s rounded bands as the moulds heat up, then for 2 or 3 rounds, it’s perfect bullets. Then, things begin to go downhill. First is frosting. Now, I don’t mind frosted bullets. Next is rounding bands and wings….rejects.This is due to the blocks being too hot.
Any time, you attempt to cast two bullets of 250 grains or larger, you will have these problems.
Then I said, John, you idiot, you’re casting too fast. Slow down the tempo and rejects go away and you get good bullets.
Why? The size of the mould blocks don’t dissipate heat fast enough and you have to have the heat with a bottom pour pot to insure proper filling of the big cavities with a sufficient flow.
About this time of big calibers, I ordered a .375 mould from Walt Melander at NEI. Talked with him on the phone and told him I wanted a meehanite double cavity. A spitzer in 300 grains and a RFN at 320 grains. He said, I can make it but don’t think it will cast. Was off the phone about 5 minutes and said, won’t make good bullets. Too much hot lead. Can I cast one cavity at a time. Yes, that will work. So I ordered it and when it came, Walt was right. Had to cast one cavity at a time.
This is one place that aluminum outshines iron moulds. It dissipates heat faster than iron does. Works well for large bullets but works against you with .22 calibers.
There are several ways to work around this problem.
The first is to time your casts. Maybe a bullet every 30 seconds. Even slower if necessary.
The second way is to use a cooling fan. I made one with a small cooling fan for a computer. Sitting a wet rag under this air flow and siting mould on it for a few seconds works to keep the temp of the mould down.
The third way is radical but works but we deemed it as impractical. We attached electrical equipment aluminum heat sinks to the mould attachment screws. It worked but made the mould clumsy to cast with due to added bulk.
The second method works the best for me./beagle
