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...