My oven is a little optimistic too, but the temps within are stable regarding one area to another. There is some variation between on and off cycles too. So I marked the dial for a peak of 400F and added a little time like Smoke described to make up for the lower temps around the off cycles. Like Gremlin noted, the "load" of lead in the oven gets hot on the outside first and it must take some time to warm all through. So I do not pre-heat, but let the oven and boolits warm-up together figuring to get a more thorough heating. Then, when the powder is all melted, I give it a good 15 to 20 minutes. Seems to work well with 7+ pounds of boolits on two trays in a little convection toaster.