I use a five by five piece of soft steel, 3/8" thick to put on top of a hot plate to keep my molds hot when casting.
Before I could replace my oven that died, I thought that coated bullets stood on the steel place would cure from heat convecting up from the steel plate.
I tumbled some Lee 200 gr. SWC bullets in Eastwood light Ford Blue powder. I lined the top of the plate with parchment paper and stood the bullets on the steep plate while the hot plate was cold. When done, I turned the hot plate on high for 5 minutes. I turned it down to low for ten minutes. I unplugged the hot plate and let the bullets cool.
Of the 80 bullets that I loaded on the plate, all were well coated and ready to shoot except for 4 or 5 that had slumped.
The parchment paper burned in the center of the hot plate telling me it got a lot hotter than 400 degrees. Next time I will try non stick AL
One bullet from the center of the plate and one on the edge both passed the hammer test.