I looked high and low but I cannot find the groove dimensions for S&W RF models with the aux cylinder options. A member has posted about having a cylinder rebored to WMR and I know that the mag is a small bit larger but I'm curious about the barrel diameter.
22 Long Rifle: "SAAMI specifies a nominal bullet diameter of 0.2255 with a tolerance of -0.004, while the specified bore diameter is 0.222." Groove diameter should be .223. In reality they'll vary a little. WMR is .224 but a little more or less too. I've never had a problem shooting 22 WMR in 22 LR S&Ws or Rugers or Colts.
minus .004 sounds like a recipe for leading. No wonder .22 rimfires show a preference for different brands of ammo. I suspect that the low velocity of 22's contribute to the lack of leading problems. When you get the velocity up to WMR levels the jacket saves the day.
I used to own a Ruger Single Six Convertible that shot 22WMR ammo fairly accurately but not 22LR ammo. Ruger told me that because a 22WMR bore is slightly larger the 22LR bullet fits just loosely enough to degrade accuracy. I guess that given manufacturing tolerances, shooting 22WMR ammunition through a 22LR bore could cause excessive pressure if the tolerances were off in the right direction. But many others have stated that their convertible revolvers shoot both types of ammo accurately.