Learn to slug your bore and chamber throats and to measure them carefully with a
micrometer and
not a caliper, which typically doesn't have enough accuracy or resolution. Slugs through barrels with odd numbers of grooves, like your S&W, are more difficult to measure and require additional equipment, like a V-block and depth micrometer or else a lathe and indicator to measure groove impression height or else a set of gages with precision holes.
Dardas cast bullets will measure them for you for free if you aren't equipped to do it.
For revolvers, many report sizing bullets to match your chamber throat diameters or not more than half a thousandth smaller than the throat diameter is the best approach for accuracy (and allows easier chambering at speed than an exact fit does). Ideally, though, you want those chambers over groove diameter. There is disagreement, but I think about 1.5 thousandths over groove diameter for commercial cast bullets sold as 1 thousandth over groove is best. However, I personally prefer chamber throats about 2.5 thousandths over groove diameter for cast bullets, and size the bullet 2 thousandths over groove. I've found that to produce the smallest groups.
Occasionally you get a revolver where the groove diameter is larger than the chamber throats, and that's a disaster for accuracy and it is common to get chambers reamed to SAAMI standard maximum diameter to correct that. It also is not uncommon to get a revolver with throats that aren't all exactly the same size, like they weren't all reamed with the same finishing reamer. The cure is the same as above.
Back in the 1980's I bought Ruger Redhawk. The store had three in stock, so I was able to make a comparison and pick the one with the best timing, the best alignment of the chambers with the bore, the most uniform barrel/cylinder gap, etc. With 240 grain jacketed soft point factory ammo, five chambers shoot under 0.7" at 50 yards off bags with a scope sight, while chamber 6 is always low and right, opening the group to 1⅝" at 50 yards. I could ream the chambers to get them all the same, but have been concerned I might upset the near perfection in the first five, so I've never done it. For target work, I just leave a plastic snap cap in the errant chamber and don't use it.
A friend of mine was so impressed with my gun, he bought an identical model (I wasn't there for the purchase, so I don't know what he could or couldn't check). It would not stay in 12" at 50 yards. I didn't have the opportunity to slug the chambers before my friend sent it to Ruger, but he sent a letter with it explaining how well mine shot (to show he wasn't a flincher complaining about a gun he couldn't control) by comparison. About 5 weeks later it came back with a note saying the shop had reamed the cylinder's chambers. The nice thing about having them do it was they refinished the cylinder in their bluing tanks so it matched the finish of the rest of the gun. We took it to the range, and while didn't shoot quite as tightly as mine, it did stay within about 2 inches at 50 yards, which was a huge improvement and more than satisfactory for the hunting he intended to do with it. So getting the chambers right is a big deal. It is probably the single most common first step taken in revolver accurizing.