[carguychris]

Whew! Ya gotta be fast to get in here before carguychris, but it's all folly anyhow because he can do a much better job at it...

Relax! You did good. Well, except one thing that's kinda got me confused...

The 2nd Gen guns typically can be spotted by the raised rib on the left side of the frame by the top rear of the grip area.

I'm not quite sure what you're talking about! Here's my list of 2nd-gen spotting features.

• 2nd-gens have visible metal backstraps and separate grip panels that attach with screws. This is IMHO the most prominent and unmistakable distinguishing feature. The 3rd-gens have wraparound one-piece plastic grips that attach with a pin at the lower rear corner. (There have been a few aftermarket wood grip units marketed for the 5900-series, but these still wrap all the way around and attach with pins rather than screws.)
• The 2nd-gen front sight is integral with the slide, whereas the 3rd-gen front sight is dovetailed.
• The red dots indicating that the decocker/safety levers are in the FIRE position are on the slide of a 2nd-gen but on the frame of a 3rd-gen.
• The RH-side decocker/safety lever on a 2nd-gen, when present, will usually be attached with a large, prominent, and somewhat unsightly Allen-head or Philips-head screw. Very late 2nd-gens and all 3rd-gens use a much more clean-looking tab that fits into a slot and is retained with a hidden spring-loaded plunger.

In terms of standard-production M5906 non-TSW production changes, there are 3 important ones.

1. In 1990, S&W switched from a vertical blade-style rear sight on the fixed sight pistols to a steeply slanted Novak Lo-Mount sight. The optional screw-adjustable rear sight was not changed. (Make note that the three types of sight do NOT interchange due to different-sized dovetails in the slide!)
2. Around 1992-1993, S&W changed from the square trigger guard to a round trigger guard. Round guard pistols will generally fit in square guard holsters but NOT the reverse. FWIW S&W later made a couple of minor changes to the shape and checkering on the round guard, but these changes are subtle and probably inconsequential unless you're a collector.
3. Between 1993-1996, S&W started using MIM hammers and triggers on many 3rd-gen pistols, and by 1997 they seem to have switched to MIM more or less exclusively. (According to collector research- i.e. "this is what my gun has on it, how about yours"- there does not seem to be a hard-and-fast cutoff date.) Unlike the constant wailing and gnashing of teeth about MIM on S&W revolvers, most 3rd-gen fans seem to agree that the MIM parts were a Good Thing, because they give the MIM guns smoother, more consistent, and seemingly lighter triggers. The MIM parts can be ID'd by mottled dark grey finish, skeletonized or cutout sides on the MIM hammers, and a slightly different shape to the step at the top of the MIM triggers. (Be aware that dark finish is NOT a surefire indication of MIM on stainless guns, because S&W also used 5904-type blued parts on the stainless guns from time to time!)

Hope this helps!