I have used the RCBS 20 pound pot for the past 20 years or so. I return all of the still hot sprues back into the pot and preheat one pound ingots on top of the pot. i try to keep the pot nearly full and adding a pre-heated ingot doesn't seem to affect the bullets. I also use a SAECO pot but noticed that adding pre-heated ingots shows more affect than with the 20 pound RCBS. Not much good to say about Lee pots.
I preheat my moulds on an electric hot plate with a 1/2 inch thick steel plate between the mounds and the calrod. This allows you to pause the casting session and resume w/o any bad bullets.
