A couple of weeks back I was teaching a friend the basics of casting. We started to have a problem with one of my mods that I have not seen before. This was with a Lee 90310 mold, a 200Gr SWC, six cavity. Normally I drop boolits that are 203 grains, but these were coming out about 205 grains. I am not aware of any change to my alloy. I was using the same recipe, from a batch of 500+ ingots from range lead with some superhard and tin. I have had good luck in the past with this alloy. I did notice that I had to turn my pot up a little, as the weather was about 35 - 40 degrees in my garage that day with the doors open and a fan running. So the boolits were dropping a few grains heavier, and on occasion the mold was not closing all the way, we were getting thin flashing on the boolit where the mold came together. The mold was also occasionally sticking together at times. Together we ended up casting about 2400 boolits that day.
I normally drop my boolits in a 5 gallon bucket of water. While I was not watching my friend after he got going, I am wondering if there was some water that may have splashed on the mold. Normally I may get a drop here or there from boolits droping in the mold, but I am wondering if he may have had some water that splashed on the mold that caused it to warp?
The mold did not appear to be damaged, and a visual inspection did not reveal anything.
How many boolits can one reasonably expect to get from an aluminum mold before it starts to wear out? Or do they not wear out? Any ideas on things that I should check?