[carguychris]

The recessed or counterbored cylinders were dropped from centerfire Magnum K & N frame revolvers ca. 1982 but NOT from the rimfire models. All standard-production post-1935 .22-caliber rimfire S&Ws have recessed chambers, including today's production. (S&W did, however, drop the pinned barrel from the rimfires along with the centerfire models.)

The L frame .357 Magnum models- the 581, 586, 681, and 686- entered production in late 1980, but were non-pinned and non-recessed from the start. There is no such thing as a "Pinned and Recessed" or P&R standard-production L frame.

[EDIT TO ADD] The recessed chambers on the .22 rimfire models are intended to contain a case-head failure and prevent the case head from separating from the case body and making manual extraction impossible. This is far more common with soft rimfire cases than with modern centerfire cases. The reasons for using recessed chambers on the centerfire Magnums- and, in turn, the reasons for deleting them in 1982- have been hotly debated by S&W enthusiasts for years, but I tend to agree with the opinion that the feature was primarily cosmetic, and was removed to reduce production costs.