That looks like a straight-taper Colt New Service barrel to me. I think NS shank diameter and thread pitch are different from N-frame S&Ws, so if the frame has been modified to take that barrel, you may need to put a reduction sleeve in there before installing a true 1950 barrel.

That looks to be a six-inch barrel. Maybe that's the original length, but I believe some of those Shooting Master heavy barrels were 7.5 inches long, so 1.5 inches may have been lost if I am right about the identification. That cut would necessitate the new sight. I agree that the one there now looks like a drift-adjustable front rifle sight.

Even allowing for compression effects from contact with the hammer stirrup and trigger rebound slide, that W spring seems to be tweaked. The arc of the front leaf and the shape of the forward bottom loop just look wrong.

Restoration will be an interesting project. If it isn't absolutely necessary to create a correct Pre-26, a shorter barrel from a later gun would make a more general-purpose .45 out of it.

EDITED TO ADD: I just realized that I am kind of interested in these N-frame "alphabet" springs. If anyone has a spare U or W mainspring (no offense, but not this one!) that they would be willing to see move along to a new home, please PM me with details.

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David Wilson