Most of us use 1:14" Some have tried 1:12, 1:10, stock is 1:161/2" in most S&W's. If your shooting only 148 HBWC suggest as other guy did 1:14 for 158 SWC's 1:12 might work a little better, depends on the speed you send it at. Several things greatly affect accuracy in these precision pieces... ammo, crimp,bullet, cylinder diameters, throat angle and depth, how hard the primer is struck to cylinder stop fit. Barrel muzzle crown needs to be sharp, and keep the forcing cone clean will help.
Most will shoot around 2 1/2" but in over 25 years of playing at it, 24 shots in 1.023" was the best I was ever able to obtain, an exceptional PPC gun can do around 1 1/4" with proper ammo tuned for it, with many in the 1 1/2" to 2" range.