Seems to me the hammer stud and trigger spring stud are polished flat to the frame on the postwar guns. That's a finishing change rather than an engineering change, but it is a treatment that continues with the short-action guns introduced in 1948.
I actually think the hammer stud change should be considered a
minor engineering change. The reason the later studs are polished flat to the frame is that they are
pressed in place, whereas the earlier studs were
screwed into a threaded hole in the left side of the frame. That management order was issued on January 18, 1946, and seems to have been implemented rather quickly. By at least April of 1946, it appears that all new K frame .38 M&P revolvers were shipping with the pressed hammer pivot stud.
most of them have the knobless ejector rod
The order to eliminate the extractor rod knob and replace it with a knurled end on the extractor rod was issued on October 4, 1946. This applied, of course, only to revolvers fitted with a barrel of longer than 2", since this type of rod was always used on the short barreled revolvers. Unlike the change to the hammer stud, this change did not seem to show up very quickly. The data I have so far collected show many guns with 4", 5" and 6" barrels with the knob for quite a while before the knurled end starts appearing. The lowest serial number I've encountered so far is on a 5" gun and it is S875065 and I believe it shipped in January, 1947. I show several with higher serial numbers that still have the knob. It doesn't finally disappear for good until the S882xxx range (about April of 1947). And I have actually located one in the S903xxx range that has the knob. That one seems to be a flier.
Many people on this Forum have contributed to my collection of data on these S prefix guns, and I greatly appreciate their cooperation. I'll once again issue a call. If you have one or more S prefix M&P revolvers in your collection that you have not reported to me, please consider contacting me about them. I have a short questionnaire I can send you so I can add your data to the spreadsheet.
Thanks!
