I had a 4.6" commemorative Ruger Single Six over six years ago and chrono-ed the following through it - from the appropriate cylinders:

.22 LR Federal GameShok 1,023 +/- 20 fps

.22 WMR Remingto HP 1,470 +/- 39 fps

The WMR's had the familiar supersonic 'crack' - which they should still have from the 2" 351PD, just a bit slower. Mas Ayoob, I believe, has said the 351PD is a decent back-up gun. Don't expect a good trigger - rimfire primers require more oomph - and the lite weight seems to enhance the heavy pull 'feel'. Be careful with hammer spring changes - make sure it still goes bang reliably! And - no S&W rimfire, J or K frame alike, should ever be dry-fired without snapcaps or spent cases in every chamber.

Stainz

PS Include centerfire type caliber revolvers in that 'don't fire without snapcaps/spent case' caution if the OEM FP was replaced with an extended reach (longer notch) FP - the repeated flattening of the FP return spring will eventually break that spring.