Hmm I can add one thing real quick
Its my own version of the blow test.
First off, you should have a rough idea of what bore size the paint is, if you have no idea ask the shop-owner, most of the time they know about what its supposed to be.
Take the nearest bore insert (back) you have and insert a ball into it. If it falls through, note it. If it stays in the back of the barrel note that. If it does stay inside the barrel, I do two diff things. The first thing I do it hold into the back of the barrel, were the ball is sitting, and flick it forward real fast. I use that to simulate running with the gun and having your elbow flex. Next, I blow on it, not a steady push, but a nice POP, and the balls should come right out onto your hand. IF it doesnt, push it a tad w/you finger, remember the balls arent perfectly round. Try it again, still no go? Bust out the squegie.... Now, do the same thing with about 10 diff balls, from diff bags if you can (some paint comes with ties, some are sealed) and mark it down. Also, use balls from the top AND bottom of the bag.
If more than any 2 rolled out, go down one bore size. Repeat above.
If less that 2 rolled out, note that bore size and the one just bigger. Try the bigger one with the same test, and see if you can get optimized results, if not, ya got the best match you are gonna get.
I usually like to redo the match everytime I switch bags, the exception of course being when I shoot more than 500 a game and have to mix it up