Yep, the box-type rails of the TSW are thicker and a bit tighter in tolerance. This contributes to the potential for some better accuracy.
A barrel profile change made for sightly delayed unlocking in the TSW, which some folks might notice as contributing to a slightly reduced recoil impulse.
Later on they added the loaded chamber visual inspection port in the barrel tab and machined the 2-step cut in the slide, under the left side decocker lever, so the optional spring-loaded, decock-only assembly could be installed, if desired.
Aside from some of the noticeable exterior changes, S&W has been making some continuing changes in design and manufacturing in the TSW models, as well.
The current 4566TSW no longer has the forward angled machined slot under the ambi lever, and the inside of the slide has had at least one potential stress spot relieved where the firing pin channel and the ejector depressor plunger channels connect at the rear. (I first noticed this in the .45 series, from one new production lot to another, and when I asked about it I was told it would eventually be done across the whole TSW model line.)
The .45 TSW barrels received a couple more revisions something like 3-4 years ago. The most noticeable was machining the barrel lug only on the top of the barrel, instead of all the way around the barrel. I didn't notice that until I had a pair of new 4566TSW's disassembled on the bench and happened to see the difference. Again, a call back to the company confirmed some recent design & manufacturing changes (including the way the feedramp was machined and how the rollover point was shaped, as I recall).
The difference in your hammers is that the one with the tub-shaped recess in the sides of the hammer is MIM and the other one is the older machined/black carbon steel. (They were still using & shipping the machined carbon steel hammers for the Value Line models even after the MIM hammers were in use for a while.)
See the 2 machined hammers on the left in this picture? The one of the far left is the older version, flash-chromed and with some serrations on the top of the spur. The 2 on the right are MIM.
If you look under the slides of each of your 3913's, to the right of the pickup rail (under where the extractor recess is located) you can probably see how the narrow slot ends in an angle, or uneven shape in the older 3913. Maybe. The shape of your 3913 ejector appears to be of a newer revision, so maybe your slide was made at a time with the newer machining being used. Dunno without handling and looking at it. The newer TSW was probably made after they changed manufacturing techniques, though, and were able to cut that slot more cleanly & evenly under the extractor recess, meaning at the end (rear). (This is why some of the older 9's sometimes would develop had a curved "crack" at the rear of this slot, because the very thin bit of metal not machined out at the floor of the extractor recess, at the top of the groove to the side of the pick up rail, could crack under recoil. The "crack" would start at the rear end of the slot, inside the thin bit of remaining metal comprising the bottom of the extractor recess, and curve outward until it reached the solid part of the slide where it stopped. It wasn't a problem, either. Sometimes the small bit of thin metal would break off and fall away and sometimes it would remain, but no longer under stress.)
These are just some of the things I can think of off the top of my head, all of which I learned in armorer classes or by talking with folks back at the factory.
Nice pictures, BTW. Mine never turn out nearly that nice.
3913TSW vs 3913 frame comparison pics
Linear Mode
