My understanding of ruger is after they came out with the convertable single six they made all .22 lr and .22 wmrf the larger bore of the .22 wmrf. The first early .22 lr single sixs are said to be more accurate than the later overbored ones. AND I really dont belive ruger, colt or S&W have built the smaller .22 lr bore and knowinly will fit or sell you a 22 wmrf clyinder for it! Now dont confuse this with the model 53 jet! They ARE the same bore as the .22 lr. The jet is really marked and called the .22 magnum. Even on this site a large number of times I have seen people wrongly call a .22 wmrf as being a ".22 magnum"! That irks me and I read it at least weekly! Huge differance!
I have/had every gun I just discussed. .22lr colt scout, rugers both old single sixs in JUST .22lr, and in .22 wmrf, and I have a S&W model 53 jet in .22 magnum. I also once owned a S&W model 51 in .22 wmrf. I had the factory fit me up a .22lr clyinder for it back in about 1970, told them why cant they do that as ruger does? Right after that they made it a catalog option for awhile. Maybe people somewhere might have fitted up a wmrf clyinder to a straight lr barrel, but I doubt that any factory would recomend it.
Now I also own a 1890 winchester that WAS chambered for 22 WRF. The 22 WRF IS a .24 bore, NOT .22. The WRF is really the same as a WMRF but shorter, like as a .44 special is to .44 mag, or as a .38 special is to a .357. You can shoot a .22 WRF in a .22WMRF. Knowing this, and WRF ammo being hard to find and more exspendsive yet less powerfull than .22 wmrf, I had my 1890 rifle chambered to .22 WMRF. It works! My gunsmith when I proposed this to him said he had done it before, and claimed that winchester intended to later build a .32 on that frame, just never done it, and it is safe.