I want to add a pinned front sight (from SDM like on my Mountain Gun here in the pic) to my Model 57 shooter which doesn't have the pinned sight. I know this is a gunsmith job, but how hard is it?

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Vaya con Dios

I just researched the same issue for my 686 no dash. It seemed there were three choices:

Do it myself - $60, remove existing front sight (mill or file) and install Weigand front sight base/blade by drilling and tapping barrel.

Have a gunsmith do it - $120 and two month turn around time, to mill off front sight, mill slot for front blade and drill pin hole and install front sight blade.

Have S&W do it - $? plus two to three week turnaround time, waiting for price, same procedure as for a gunsmith (or they might change the barrel).

Since I had to send my gun in for a recall anyway and a few other issues needed to be fixed (mis-machined cylinder throat in one chamber, over tightened barrel, 0.008" BC/0.002" endshake, recall) I chose to have S&W do it. I live about 15 minutes from S&W and dropped it off on Monday. Because of the recall shipping back to me will be free.