Howdy
I have S&W revolvers from every decade starting in 1863. I am a purist/snob so my collection stops in the 1980s. I only own one MIM Parts/Lock gun, a Model 617. It is fine, nothing wrong with it, I just don't care for the lock and MIM parts. But there is nothing wrong with it. My favorites are the pre-war (before WWII) guns. Fit and finish seems to be the best with them.
I will say the first two Smiths I ever bought were a Model 17-3 and 19-3 that I bought brand, spanky new in 1975, during the Bangor Punta era. I have read lots of bad press about the Bangor Punta era guns, but there is nothing at all wrong with mine. Internal finish of the parts is excellent. On the inside it is apparent from the milling marks that the frames were made with CNC equipment, while earlier frames show tool marks consistent with hand operated pattern following equipment. I have to say, the CNC made Bangor Punta frames actually exhibit a better finish inside than some of the earlier pattern following frames. Much more consistent finish. However, it really does not matter because the rougher surfaces left behind by the pattern following equipment are all clearance cuts anyway, nothing to interfere with the moving parts.
Here is a shot of a frame cut with a pattern following miller.
Here is a shot of a frame cut with CNC.
The bottom line is it really does not matter, because most of the moving parts don't bear on the frame. The rebound slide and cylinder latch do, but they glide over the tooling marks just fine anyway. But I think it is an interesting point that the CNC finish is so much finer. That's what programmable machines can do. By the way all the makers use CNC equipment today, and that does not guarantee perfection. Uberti in particular sets their feed rates too fast, to produce more parts per hour, and the finish on their parts shows it.
Please Note: The bottom photo is not of a 1975 era Smith. Old Fuff caught my mistake, explained below.