bore dimension

You need to slug the bore using a soft lead ball. Do a search on cast boolits or a similar reloading site it will probably come up with a thread on how to do it its a question that comes up fairly regularly.

if you are really really really really good with calipers you may be able to come close on your bore dimensions by trying it in the end of the barrel.

If you slug with a soft lead sinker wt, use lots of oil, to help slide it through.

or you can try what most try and that is just go about 1 thousandth over the nominal bore and see what happens. For most modern (recently produced) firearms this will work as a decent starting point. If it’s an old milsurp, all bets are off.