That 10 minute time starts when the bullet reaches 400 deg but thick heavy bullets take longer. The recommendation to start the clock when the powder coat looks wet is workable, but more time is needed if the bullets are heavy.
I haven't seen any down side from over cooking. Under cooking causes incomplete curing so cycles will run 20-30 minutes.
My oven only hits 400 if the dial is turned all the way up to 450. I use a fiberglass wrap for better efficiency, and there is a lot of heat loss from the window so I cover that too.
I use a BBQ thermometer in the oven to know what the temp really is.
Water dropping may not be necessary or desirable depending on the bullet performance you are after.
