Hmmmm.....external diameter of the powder bushing would it not be 0.002" < than the charge bar hole for the bushing? As for the height equal thickness of the charge bar? Inside diameter will determine the powder charge so reaming the bushing a few thousands at a time while weighing the powder...
I have been lucky with Speer to Sierra, get the distance correct, if the powder charges are in the same range, load and shoot. Always been good for me. Perhaps Sierra to Speer will be kind to you Sir.