If you don't elect to send your pistol to Bar-Sto and have them fit the barrel at the factory, then a, 'semi drop-in barrel' is the way to go. Both of my Glock Bar-Sto barrels are semi drop-in. I did the final minor fitting myself with a set of diamond knife sharpeners, a felt polishing wheel, and a Dremel Tool.
An extremely tight fitting barrel isn't necessary on a Glock - any Glock! (The rest of the pistol wouldn't keep up with such tight tolerances, anyway.) The semi drop-in tolerances are more than acceptable. If you're, in the least, mechanically inclined this is an easy and fun thing to do.
If you don't want to attempt final fitting, then, you have the option of buying 150 rounds of healthy SD ammo and shooting your new barrel in by pounding everything into place every time the pistol recoils. (NOT my preferred method of final barrel fitting!)
90% of the fitting takes place at the end of the barrel hood where it makes contact with the slide. The amount of metal you have to remove is very slight - Rarely more than .001". You need to take pains to maintain a straight edge. I used a small machinist's square; but, I've known people who just placed the end of the hood against a flat-lying piece of window glass - Which works just as well.
The final step is to polish up the work area with a felt wheel and either Flitz Polish or white (fine grit) jeweler's rouge. The whole process should take you less than 2 hours - And this is working very slowly and carefully. My first fitting job took me, almost, 3 hours; my second fitting job took less than 45 minutes.
Funny, because the last Bar-Sto barrel that I had a big name gunsmith install with a power grinding wheel was crooked at one end and rough surfaced. I ended up having to reinstall it, again, myself.
You can, also, mark the back of the hood and vertical chamber sides with lipstick or crayon. Then open and close the slide. You will see where the HARD contact areas are. If the barrel lugs are rubbing - after cycling the slide a few times - you'll, also, be able to see where you need to do a little more touch up work, too.
Like I said: This isn't difficult to do; and the amount of material that has to come off is either very little, or NONE AT ALL! Check the final fit by eye, by appearance, or by repeatedly cycling the action and looking for rub marks.
The other thing you can do is to simply fire the pistol. (If the slide closes all the way, then, 'Why not!' Just be sure to fire only one or two rounds at a time while checking between shots to make sure the pistol has returned to battery.) I used fine grit EZE-LAP diamond knife sharpening hones. They are the perfect tools for this job.
These two tools, a light gun oil as a whetting agent, and either a powered felt polishing wheel or a hand-held Q-Tip (and a lot of hand rubbing) are all that you need to do an excellent fitting job on one of Bar-Sto's semi drop-in barrels. Fine LapSuper Fine Lap Flitz Polish