Model 48's are nice guns / like other response said, .22 Winchester magnum....K frame, Square Butt frame - and were made in 4", 6" and 8 3/8" barrels.....and this model was made from 1959 thru 1986.
The S&W catalog says the Nickel finish was not catalogued ...but they are known to exist../ since you have one - and it is rare. I have never seen a Nickel version...and a lot of collectors would love to have it, especially if its in good shape.
Just as a note, the model 648 ....is a comparable newer model in stainless - but they were only made in a 6" barrel / and were made between 1989 and 2005.
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A lot of us would love to have a model 48 ( blued or Nickel ) in our S&W collections....I do not have one / and most every one I come across has a lot of wear sadly ....
.....most of us that want one, are looking for a 4" , or maybe a 6" ....but the 8 3/8" is a nice "target" or close range "varmit" gun.