As I was reading the various responses in this thread, I was thinking that a lot of guys are making this harder than it needs to be.
I previously recommended pre-warming.
I realized that I had an opportunity to do a "quick & easy" demonstration that may get through to those reluctant to try pre-warming.
I use HF red. I keep it in my garage & take no special efforts to keep it dry. I am about 25% into my second pound. Note that I also re-use the left over powder in my shaker container at the beginning of each session.
We have had a very wet summer here in Wilmington NC. I can not even remember the last day when it did not rain. Between rains, water is oozing from everyone's yard and leaving puddles on the edges of the roads.
I went out into the garage with a batch of Lee 44 cal SWCs. Turns out the batch was 285 boolits.
I tossed the boolits into a metal tray and put them in my oven. I left it on for 1.5 minutes (readout was 150°F at this point) and then turned off power to the heating element. The readout slowly went up to 200 °F after I secured power and then started coming back down. I left the boolits in the oven for 3 additional minutes with no power. I tried to measure boolit temp and estimated it at 117 °F
I put a handfull in the shaker container with my black airsoft BBs and old powder. I would normally have added some more powder as there was not a lot left, but I did not just to see what would happen. I did a 15 seconds "swirl" and then did an up and down shake. I found the coverage "ok".
I tossed the boolits nose down into one of the trays that come with factory ammo (a range pickup, I never buy ammo). I do this as quick as I can with no special efforts of any kind. I then invert the tray with a "cover plate" and slide them off on the the cook tray covered with parchment paper (it works much better for me than the NSAF did)
I did another two rounds in the shaker container with the old powder and then added powder. With added powder, the coverage was great with a 15 second swirl. Here is the second round with the added powder.
I finshed out the full batch. Here they are ready to load into the oven.
I did my normal "cook for 15 minutes after the readout reaches 350°F" and then secure power. I left them in the over for an additional 3 minutes, then took them out. Scooped them off the cook tray and here is the result: