Bullet casting question

[Marshal Deadwood]

My bullet  mold that normal tosses .454/.453 bullets seems to have a mind of its own last casting session. They mic out at .451/.450.  I have checked my calipers on known demisions and they are right.

The only thing I can think of,,is last batch of bullets I might have cast with the lead hotter than normal. Would that make a difference ?

I admit, I'm slightly baffled.

I did recycle some bullets with lube on them that had creases or voids from previous deal and I decided to go for a better cast on them........but would that have an effect.. a bit of bullet lube in the lead ?

Never had this happen before.

MD

[Bow View Haymaker]

Did they have a frosted look or shiny?  If frosted the mold or the lead may have been too hot and might have some shrink. 
OR the molds might need a good cleaning.  They can get some buildup of crud.  A good cleaning with a wire brush and maybe some brake cleaner or commercial bulet mold cleaner can help.  We had our 45acp molds start dropping bullets that would hardly seal in the sizer at .451.  looked ove the molds and they were DIRTY. 
worth a try.

[Sir Charles deMouton-Black]

Is your alloy the same as the earlier lot?  A harder alloy casts slightly larger, and vice-versa.  Are you gripping the handles the same each time and making sure the halves mate properly each cast?

Otherwise I would check the condition of your mould.  I don't think it is a heat control issue.  I cast hot to get a a better fill out, and I've found no real difference in diameter from the bullets dropped while the mould heats up.