cast diameter growth / shrinkage

[milkman]

I have been trying to determine the cause of fliers I am experiencing and was wondering about the weight variance in my boolits. Lighter was pretty easy to explain, voids or poor fill out. Heavier was harder to get my head around. Was part of the alloy heavier in spots that would enter the mold causing heavier boolits? Was there dross that was heavier and settling to the bottom and being pulled through the spout into the mold?

After a gentle push from Idaho Sharpshooter I cast a batch of boolits, keeping track of them as they came from the mold and was really surprised at what I found. The weight variance was almost exclusively related to the diameter of the boolit.

Here is a list of the boolit weight and diameter in the order they came from the mold. The warmer the mold, the larger the boolit. My pauses during casting show as reduced diameter, then growing again as the mold warms. The file is not really plain as I was using a double cavity mold and some rejects were thrown into the reject pile with the sprues, but a clear progression to a .003 larger boolit is shown, and I was trying to keep the mold at a steady temperature by timing the sprue freezing. Weights for the same diameters seem pretty consistent.

[sqlbullet]

That is consistent with what I see. I usually sort my cast boolits in 1 grain increments if I am going to shoot them for accuracy. Mostly I just reject the ones that fall outside the .5% variance, as that is usually only about 10-15%. Those go in the "plinking" pile.

[Doc Highwall]

I bought a thermometer with the probe from Al at NOE that attaches to the bullet mould so I can monitor the temperature of the mould as I cast.

I preheat the mould and I know what temperature I need it to be to get good bullets the first pour. That with the PID controller from Frozone and a little record keeping goes a long way.

It is like casting in the 21st century.

[44man]

I have been trying to determine the cause of fliers I am experiencing and was wondering about the weight variance in my boolits. Lighter was pretty easy to explain, voids or poor fill out. Heavier was harder to get my head around. Was part of the alloy heavier in spots that would enter the mold causing heavier boolits? Was there dross that was heavier and settling to the bottom and being pulled through the spout into the mold?

After a gentle push from Idaho Sharpshooter I cast a batch of boolits, keeping track of them as they came from the mold and was really surprised at what I found. The weight variance was almost exclusively related to the diameter of the boolit.

Here is a list of the boolit weight and diameter in the order they came from the mold. The warmer the mold, the larger the boolit. My pauses during casting show as reduced diameter, then growing again as the mold warms. The file is not really plain as I was using a double cavity mold and some rejects were thrown into the reject pile with the sprues, but a clear progression to a .003 larger boolit is shown, and I was trying to keep the mold at a steady temperature by timing the sprue freezing. Weights for the same diameters seem pretty consistent.
As a mold gets to the right temp, it will make consistent boolits but as you get hotter and hotter, boolits will get SMALLER. The ideal is an even temp for all boolits.