I have a 5 cavity NOE mold in 6mm.  The instructions that came with it say not to run the lead over 600 F.  I tried that but the bullets do not fill out.  I cast about 80 and 4 of them look usable but don't quite come up to weight.

Then I ran the temp up to 700 and cast another 50, all of which run within .2 gr of each other.

Is there really a problem with a 6mm mold and running it hotter than 600F?

I could see that with a large mold like a .40 or larger but am curious as to what could happen to a large block of aluminum with such small holes in it.

I had a 4 cavity 25 cal NOE that I cast at 800 degrees. No issues except with a large spru overflow it was too hard to open the plate by hand and needed a whack. I would usually only use the back 3 cavities. 

Jack

Are you folks casting with aluminum molds?  I've never owned a NOE mold before and I can't tell from their website if they make the 3+ cavity molds from steel or brass or only aluminum.

Meanwhile I cast 150 bullets this morning at 700+ and they're all nicely filled out and of plus/minus .2 of each other.

Wish I could get that many equally even weighted bullets out of my .32 molds with as little work