I just reamed 5 cylinders (22 LR) yesterday with the same Brownell's finish reamer. Two M17, two M617, and M18. The M18 was first, patience, lots of cutting oil, frequent cleaning are keys to success. Each M18 chamber took about 5 passes to finish because I only advanced 1/8" when reamer got harder to turn. I didn't want it binding. The M18 also has a bad barrel leading problem.
One of the M17 cylinders had been reamed by a previous owner. The 6-shot M617 cylinder was the "most difficult" to ream because of the amount of metal removed. The 10 shot M617 cylinder was the easiest because the chips were almost dust and the reamer never was hard to turn.
EDIT: Range Report
My five 22 LR revolvers were OK after reaming. 5 barrels were spotless after one pull of the Bore Snake, just like every chamber. The M18 fired 3 boxes of different 22 LR ammo to see if it would lead up. It didn't.
The range targets are four 3" bullseyes with scoring rings (reduced 25 yard bullseye targets) on a 24" x 48" sheet of paper. After shooting all the revolvers with different brands of ammo, I took a box of Aquila Super 22 LR and fired each gun at the same bullseye hung at 11 yards, than checked the target, and marked the misses.
Each gun had 4 or 5 of the shots in the orange center [3" group] and all of the shots were inside a 4" scoring ring. My conclusion was the reaming was successful for accuracy and ease of loading / ejecting cases. This 'accuracy' target was fired after 3 hours of shooting on a 90° indoor range. It's been warm in Georgia.
EDIT 5-17-20: I bought a M34-2 off GB, J-frame 22 LR snub with 2" barrel. I loaded it with Federal, Remington, CCI, and Aquila ammo. Cartridges dropped right in, empty cases fell out, accuracy was very good with no leading in the barrel. I think S&W got smarter or better.
