Bore diameter

[popper]

Just tap a cast bullet into the throat with wood dowel and then tap out with coated cleaning rod. Cheap 'pound cast'. Measure where you see engraving marks. Pound harder and you get throat size.

 

[fiver]

you can always sand down a wood dowell until it fits too.
your not gonna get three decimal places,, but your not gonna get that from a mold or size die either without other tools that would make a pin gauge set seem cheap.

I think all Kevin needs here is a 300 or 301 type measurement.

 

[358156 hp]

I used to just tap a two-diameter cast bullet into the muzzle to see how it fits, then I'd do the same thing from the chamber end, only until the rifling engages the shank portion. It was handy to use a slightly larger caliber bullet for this because I wanted to see what any engraving looked like. I suppose an existing mould could be "beagled" to increase the bullet diameter for this as long as you remember that you're dealing with a slightly ovate bullet. Just tap the bullet into place and back out at both ends as fiver suggested. To measure a bore riding nose I would think a caliper would measure close enough for this purpose.