Bore and throat slugging is the easiest to do with pure lead slugs.
Merely cast up some that are oversize, or in the mould for that calibre. They do not have to be perfect like bullets you want to shoot - wrinkles are fine.

Clean the barrel and oil, then push 1 or 2 dry patches through to fall off the jag at the muzzle. Slug the bullet up a bit with a hammer, then pound it into the bore and down a 1/2 inch or so - or into the throat and stop just into the rifling. I use Hickory ramrod sections for this to prevent damage to the muzzle or chamber. Insert a rod, hickory or cleaning rod with a blunt end from the muzzle to contact the 'slug in the chamber, or from the breech to contact the one at the muzzle. Insert another rod from the other end and pound on one of them with the other supported to the lead slug is mated to the area you want to measure. Push the slug of lead out with a rod in the direction of the shortest way and measure it - groove diamter, land diameter or diameter and length of lead/freebore, angle of throat and length of same. Pretty simple, quick - and accurate. Do NOT use hard lead for this - pure or almost pure lead only.

In the time it took to type and/or read this, I could have done a barrel, easily.

500gr. + .458 bullets work well for .40 to .48 cal., for instance. Always keep some pure lead bullets of various sizes on hand for 'new' aquisitions.