.22 combat masterpiece
Early in my police career I carried a S&W 15 .38 as a duty gun.
I bought a S&W 18 as a sub caliber trainer gun.
Worked out really well. I'd take both to the range and warm up with the .22 before breaking out the "big gun". And for a while we could shoot at the local Army National Guard armory range, with was indoors and limited to .22 only, and I shot the model 18 a LOT. A 500 rnd brick of Remington golden bullets was only $9 in the olden days.
My model 18 has about the nicest double action trigger of any revolver I've ever fired.