Sunday, June 04, 2023

Sunday Smith #73: Model 639, 1984

From its introduction in 1955 until its production ended in 1982, Smith & Wesson's first generation of single-stack nines saw only minor changes. In 1957, it became the "Model 39", with some improvements to the extractor and safety lever. Then in 1971 further design changes to the extractor and feed ramp rated the "Model 39-2" nomenclature.

Starting in the early Eighties, Smith began marketing a whole new generation of its pistol, and added a third digit, so the aluminum-framed Model 39 with its carbon-steel slide became the Model 439, and the same gun with a carbon-steel frame and slide was the 539.

In 1984, Smith leveraged its experience in working with stainless steel revolvers into an all-stainless version of its 9mm pistol: The Model 639. This was something of a novelty at the time, since Smith was one of the only manufacturers of the era who sold stainless self-loaders that weren't plagued by galling issues between the frame and slide.

The most notable change in the mechanicals of the Second Generation pistols was the addition of a firing-pin safety that rendered them more drop-safe. They also had optional ambidextrous safety levers, a checkered backstrap, and the adjustable rear sight on models so equipped was protected by sturdy "wings" rendering it less likely to be knocked askew when carried in a duty holster or dropped.

The first few hundred 639's off the line had a short, wide extractor before it was changed back to the proven type found on the 39-2. After the first year of production, 1985 and later guns had a square, hooked trigger guard of the sort that was popular in the '80s. Those two factoids (plus the "TAA" serial prefix) date the 639 in the pictures to 1984.

Notable Hollywood 639 toters include The A-Team's "Hannibal" Smith and Harvey Keitel's Mister White in Reservoir Dogs.

Production of the Model 639 continued through 1988, when it was replaced by its heavily-revised Third Generation successor, the Model 3906.

The pictured pistol was acquired from Indy Arms Company for four fifty in summer of 2023.


Blackwing1 said...

How did S&W (and now other manufacturer's of SST pistols) get past the galling and binding issues with stainless steel?

As a (now-retired) engineer one of my responsibilities used to be for the literal nuts-and-bolts of my division's usage. We always had an issue when a customer mandated stainless fasteners, particularly Type 304, when they would attempt to assemble them with high-speed nut drivers or impact wrenches. If you assemble SST fasteners as low speeds it's usually not a problem but galling and binding would almost always occur at high assembly speeds. Our recommendation for lubrication was pretty much universally ignored in the field by the steel workers. We found we could avoid the issue entirely if the customer would allow us to use slightly different alloys of stainless for the nut and bolt, as long as the strength matched.

So I'm curious how the firearms manufacturers got past those issues, if you happen to know. My quick exercise of my (poor) Google-fu skills show kind of that same answer of different alloys between frame and slide.

Ben W said...

I’m (another engineer and) also curious what kind of stainless steel they use on pistols. I suspect they use a 400 series, which tend to machine better and be a bit less gall-prone than the 300 series. I doubt they’re using something as expensive as 17-4PH. I know BAT machine makes their rifle actions with stainless bodies and carbon steel bolts to avoid galling, and bolt actions see much lower speeds than reciprocating slides on pistols.

Matt Donahue said...

One of my biggest regrets in my career as a gun hipster, is that the 39-2 I briefly owned wasn’t reliable. It was a deliciously shootable little blaster—very intuitive ergos and trigger. Slightly better than the 3rd gens I’ve owned, honestly. Mine was an earlier example, with the flatter bushing and the hole in the hammer. Maybe a later one would have been better? I don’t know. But I DO know I now want a 639. Thanks for the tactful enablement.

Ed said...

"The pictured pistol was acquired from Indy Arms Company for four fifty in summer of 2023."

Summer Solstice will be in more than two weeks, but many consider Summer to be between Memorial Day and Labor Day.

Blackwing1 said...

Reply to Ben W.:

We found during our salt-spray corrosion testing that Type 400-series SST's (particularly 410) were all extremely prone to surface corrosion. They would generate a really ugly rust look on the wasn't deep, and once the surface oxidized it pretty much stopped, but customers hated how it looked. The good part about Type 410 was that it could be made hard enough for self-tapping screws for use in carbon-steel sheet metal, while the austenitic alloys (300 series) couldn't.

Everybody seems to think that SST is always stronger than carbon-steel when the opposite is the case. To get really strong (on the order of a Grade 5 bolt) 300-series fastener they have to use strain-hardened wire stock, which must then be machined into a bolt shape, which then costs an arm and a leg. It's why we don't see a lot of SST fasteners in structural applications.

If the firearms manufacturers are using 400-series SST's in their products I have to wonder how they prevent the surface corrosion that you usually see with that material. I've got a couple of Springfield Armory 1911A1's in stainless and have never seen a trace of corrosion on the slide or frame despite being carried next to a very sweaty body in a Minnesnowta ("land of 10,000 lakes and 1,000,000 swamps") high-humidity summer.