I like the concept of an "understudy", a smaller caliber gun, that mimics the frame size, weight and feel of a larger caliber gun, while using less expensive ammo, and offering reduced recoil, so a guy can practice, without breaking the bank.
K-Frame .22's are wonderful, because they are cheap to shoot, and handle like K/L-Frame .357's.
In my accumulation there are 2 pair of such revolvers. A 617 ND has the same full lug as 686-6.
And a CSP 18-3 to go with a CPD 66 ND. I've posted the 18-3, recently. It was used by Colorado State Patrol to train cadets, before they moved up to .38's and .357's. I don't know for sure, but was told that they carried 19's and 66's, on-duty.
I don't know what agency CPD is, as it was a pawn-shop buy.
The 18-3 was consigned to the LGS, by the retired trooper, who bought it from CSP when they transitioned to semi-autos.
What have you guys got, that you'd consider an understudy to another gun, in your collection?