Quote:
Originally Posted by Sevens
the long action was what was used in the older guns (pre-WWII or thereabouts) and you can see an exposed hammer pin on the LEFT side of the revolver very near the cylinder thumb piece.
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You are on the right track, but let me clear up a detail or two.
First, the "pin" is the end of the threaded hammer pivot stud - it was threaded into the frame's left side. The later type was pressed into the frame and polished flat during the finishing process.
Second, the threaded stud went away on the K frames in 1946, approximately two years before the "High Speed" hammer was introduced into production. So there are a bunch of S prefix M&P revolvers with the pressed stud and the long throw hammer.
Details:
The change order for the hammer pivot stud was issued on January 18, 1946. The pressed stud entered production at about serial number S819462. Shipments of guns using the new stud seem to have started in April, 1946.
The change order for the High Speed hammer was implemented at approximate serial number S990184. The earliest ship date I have for an M&P with the High Speed hammer is March, 1948.