And sometimes it's the ammo...

[Half Moon]

I recently came into a small collection of Smith & Wesson Model 12 Airweights - a pair of 2" snubs and a full size 4". Now the snubs were perfectly fine but ole 4" he's been another matter. Severe binding, light strikes, etc.

Light strikes was an easy enough fix with a tightening of the strain screw but the binding eluded me: ejector rod tight, b/c gap good, clean under the star, firing pin bushing level and not peened, and so on and so forth.

Frustratingly I also couldn't recreate the issue with dummy rounds. So I loaded up some spent brass, pulled the hammer just enough to drop the bolt,and ah-ha(!) it's binding on chambers 2, 3, and 5 as the cylinder came around to the firing pin bushing. Gotta be something bent, right? Except, when I shifted the brass to other chambers the problem moved(!). WTH?!?

Pull out the calipers and the cartridge rims are .064" thick. SAAMI says. 048" to .059" are acceptable rim thickness for 38 Special with allowed revolver headspace of .06" to .074" Measure some other brands and rim thickness is generally right around .058" and the brass doesn't bind.

Went to the range today with six brands of ammo. Only the Sellier and Bellot 158 grain JSP's with the over thick rims bind. Otherwise the Model 12 full size is a happy camper. Don't know if this is just a bad lot from S&B but have found at least one older thread online with similar issues. In that instance 357 S&B measuring .065" and binding a GP100.

I've liked S&B ammo historically but this a caution to me going forward...

[OlongJohnson]

This thread is useless without pics of the pair of M12s.

[Malamute]

Interesting, and not exactly surprising.

Most people arent aware of how much ammo varies within and, obviously out, of spec. One gunsmith told me that when building more precision varmint guns, he started checking factory ammo, most rifle ammo is under spec, meaning short-ish headspace specs and loose in the chamber of standard chambers (remember its a range of allowable size, both chamber and ammo, not a single perfect size they all somehow mange to achieve). Getting closer to ideal max spec ammo required more time and better equipment to stay as close as possible yet still within that max size allowed, which doesnt equate into affordable ammo that most people want.

Its been recommended to check headspace in lever guns that back primers out some* by using a case and shims or plasti-gage. Add shims until the bolt wont close, remove one, measure shims, "yep, theres the problem, ya got x thou headspace", and so far as ive seen, not mentioning the rim thickness of the case to give a real reference point as to true cartridge headspace spec, which in turn would give a true indication of the rifles headspace. A gun can be within allowable spec range of headspace, a cartridge can be within allowable spec on headspace, and end up with a fair amount of nothingness in that space. all within spec. Measuring that space with no reference point of the cartridge rim thickness doesnt tell you if the end result if within allowable size, just how much space there is, and it can be in the allowable range of actual sizes.

Back on topic, go over the allowable cartridge headspace spec (rim thickness in revolver cartridges), and it may work in a looser chambered/headspaced gun, or it may not.



*The primers backing out in levers is another matter, and one not as simple as it first appears. Its not necessarily a headspace issue. Your reloading manual will indicate its a low pressure symptom with bolt guns (saying nothing about headspace when it shows up in lighter loads), but not many seem willing to accept that in a lever, it must be headspace. Its worth checking, correctly, but I now believe in many cases is fairly benign.

[Half Moon]

Back on topic, go over the allowable cartridge headspace spec (rim thickness in revolver cartridges), and it may work in a looser chambered/headspaced gun, or it may not.

And that's a truth. The S&B makes nice small groups with step-son's favored pre-15 so he was defending it today. He pointed out this lot works just fine in the Combat Masterpiece, my 640-1, and both Model 12 snubs. I've got to assume the full size 12 is close to minimum spec for headspace and the others aren't.

And for OlongJohnson:



2" round butt 12 no dash, equivalent 12-2, and 4" square butt 12-3.

To be blasphemous though I'm seriously considering selling or trading the snubs. The 12-3 reminds me a lot of my dad's service revolver (a pencil barrel Model 10). That's the first handgun I remember shooting so I'm almost feeling sentimental about the 12-3. The snubs though are neither fish nor fowl. Too big for pocket carry and not enough oomph for belt carry. Then again there's a certain cool factor to having all three.