I've been casting for years, mainly solid bullet designs.  Lately, I've been having issues with designs having multiple grooves; they seem vulnerable to temperature spikes that frost the mid-sections (where the mold is densest).  What do folks using these designs do to keep the temps within good fillout ranges?  I'm using a PID for the pot and a wet sponge to cool molds when they get too hot.

Pentz, heat the mold and melt up to a temperature where the sprue puddle frosts in 5 to 8 seconds.  Hold the temperature and maintain the same casting rhythm.  They will be completely filled out with with sharp GG bands, sharp base bottoms and look as good as these..
 
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And be sure to start with a clean mold - no smoking required and lube the pins

I don't look at frosted bullets as being a bad thing as long as the bullet is completly filled out. Some of my shooting has been with bullets showing a little frosting. I have found that a real pretty looking bullet cast at a lower temperture is more times than not completly filled out.

Just my experiance.
JLouis

I appreciate the replies, all spot-on.  The lead composition is 25:1 and it has been working great at 725 degrees for my Hoch 205.  The multiple GG mold is new to me so yes, I'll drop the temps and experiment.  FWIW the Hoch mold is significantly smaller than the  Saeco so it cools quicker.  The heavier Saeco is bigger so retains heat longer.  It is apparent that I may not be able to use both at the same session.

Pentz wrote on May 26^th, 2015 at 1:04pm:

Pentz
Looking at the image of your two bullets, it appears that neither have sharp edges to their bands and grooves and yet, one of them was frosted and deformed "sucked-in" by an overheated mold. 
Simply put, your alloy and or mold were too cold for the bullet on the left and the mold was too hot for the bullet on the right. 
You just need to learn the pace of that mold. 
I would cast with the alloy a bit hotter, allow the sprue to solidify, and i would wait a few seconds with the mold open before casting another. On such large bullets and 650-700 F alloy, i would guess 15-20 seconds of air cool time with mold open would produce good bullets and avoid frosting.  
I keep each mold in a plastic box and inside each box there are notes on temperature and cooling seconds/pace between pours. You see, i keep pace by counting. 
I also learned to use a 6" fan for cooling. I don't cast such large bullets, but with 350 grain .458" double cavity, at 60F outside air temperature, i cast 700F lead alloy, i wait for the sprue to solidify, i cool 5 seconds in front of the fan, i open the mold, dump bullets, leave open 10 seconds, etc etc   You need to learn these for your own mold/temperature/bullet/alloy. 
I would NOT use the wet sponge, it cools too fast in one end of the mold and you don't have the same temperature of the mold with each casting. I tried the wet rag method and the resulting bullet weights spanned over 3 grains. After learning to pace myself by counting and to cool with air and fan, i now cast 200-500 bullets in one seating and 90% of them are within 1/2 grain of each other.     

argie1891 wrote on May 27^th, 2015 at 9:16pm:

You may be absolutely right about the alloy needing tin. 
I have an iron RCBS 325 gr 2 cavity .458 that produces wonderfully accurate bullets in my rifle, but the two cavities are so close together and there is so little metal between them that it took quite a while to learn the casting pace without severe frosting  and deformation Indeed, i have single cavity molds that seem to cast faster. What you describe is the reason why i avoid aluminum molds. Too fussy for me. 
Have you tried alternating the cavities, say pour cavities 1 and 3 first, cut and dump, pour 2 and 4, repeat?. It may speed up casting by avoiding overheating.