Sorry for the late reply. First of all I would verify that your slugged bore is, in fact, .452. Check it with a micrometer, not a dial caliper to get an accurate measurement.
As for bullet diameters, there are several factors that will cause them to vary such as the alloy itself and the temperature of the alloy when you cast the bullets. Powder coating thickness is also never uniform. The bottom line is that unless you size the finished bullets the above variables can cause your bullet diameters to vary greatly which may, at a minimum, affect accuracy and at worst cause failure to feed/jams.
The nice thing about a mould that throws .453 bullets is that the likelilhood of getting undersized bullets is greatly reduced. If the cast bullet is thrown at .453 and you add on 2-3 thou for powder coating you are talking finished diameters in the .455-456 range which means sizing down to .452 with a Lee size die. You may have to lean on it a bit but a 3-4 thou reduction is not unreasonable. Personally i would go with the .452 size die and see how it works. If the accuracy is acceptable then you're good to go. If the rounds easily pass the 'plunk' test and you think that a slightly bigger bullet might increase accuracy then you can gradually enlarge the die. The reason i would go with the .452 instead of a .454 is that you can always make the .452 bigger but if the bullets out of the .454 die won't chamber reliably you can't make the die smaller.
The nice thing about the Lee dies is that they are not expensive so you haven't wasted a lot of money if you screw the die up or end up with one that doesn't work.
