As far as I can tell, RCBS nor Lyman make a .453" sizer die. Any ideas why?

Alan

Not hard to lap out a .452 to .453

Just use fine sand paper on a split stick

Chuck up in a drill and move up and down through the sizer die

After a few min , size a bullet to see how much more you need to open the sizer die

1/2 the time a die produces a different size than what it is susposed to
Your Alloy can efect the results

John