Skans said:
I like the fact that I can swap out grip panels on the 659, but the 5906 fits my hand better.
For the OP's benefit, I'll add some explanation here.
The plastic wraparound grip unit on a 3rd-gen S&W is retained by a pin at the bottom rear corner. The grip unit itself doubles as a mainspring retainer; the mainspring and hammer strut are supported by a metal cup that sits in a recess within the grip, above the retaining pin. Since the grip is complex in shape and is crucial to the function of the gun- it's not just two slabs of wood or plastic with screw holes in them
- there are not very many replacement options. AFAIK only Hogue offers aftermarket units today, and they're fairly bulky, which can be problematic on a gun that's not exactly svelte to begin with.
I find the stock wraparound unit to be shaped nicely, but it's rather slippery. Due to the slim aftermarket, I recommend adding grip tape, a wraparound sleeve, or a DIY sleeve made from a bicycle tube.
The previous generations of 59-series pistols used traditional screw-on grip panels and a separate 1911-style backstrap mainspring retainer. The downside is that the older grip shape is rather blocky, and is generally awkward for shooters with small hands. The 3rd-gen grip is considerably more ergonomic and comfortable IMHO.
Other 3rd-gen 59-series tidbits...
Three styles of rear sight were offered- a simple drift-adjustable blade, a slanted Novak unit that replaced it ca. 1990, and a fully screw-adjustable "hooded" or "eared" unit that's wonderful at the range but is quite large and unsightly. The three types are NOT interchangeable because the dovetails in the slide are different sizes. The entire slide can be swapped over, but I've described this as the proverbial tail wagging the dog.
If you dislike the mag disconnect, it's easily disabled, although this requires drifting the rear sight halfway out. Field-strip the pistol and look under the rear of the slide; you'll see two buttons, a metal one and a white plastic one. (I don't have a S&W handy, and I can never remember which button is on which side.) The metal button is the firing pin block; the plastic one is the mag disconnect, which works by simply pushing the trigger drawbar downwards when the mag is out, thus disconnecting the trigger. To disable the disconnect, drift the rear sight towards the firing pin block button, and lift out the disconnect button and spring as the sight clears them. Drift the sight back to center, and you're done. (I don't recommend doing this to a defensive pistol, but I wouldn't hesitate if it's solely a range toy.)
Later-production S&W 3rd-gen pistols used MIM hammers and triggers, which can be readily identified by their dark grey color, a step at the top of the trigger, and cutouts in the sides of the hammer. However- contrary to the constant
"MIM Is Evil!!!" grousing you'll often hear in reference to S&W revolvers and 1911-type pistols- many 3rd-gen fans like the MIM parts, because the trigger pulls on MIM guns are generally more smooth and consistent out of the box.
The DA pull on an earlier-production M5906 can be lightened by replacing the stock 20lb mainspring with a 16-18lb Wolff spring. The 18lb spring is almost 100% reliable, and S&W reportedly switched to this weight late in production. OTOH the 16lb spring may yield ignition problems with certain ammunition in some guns; YMMV. (The same defensive pistol disclaimer applies.)
30rd mags from a Marlin Camp 9 Carbine will work in the gun.