Bore diameter for 32 S&W & Long

I load and shoot 32 S&W long for 4 Colt Police Positive and Police Positive Special revolvers spanning from 1923 to 1955. My load is a Lee 93 gr. cast from 50/50 WW/PB, air cooled and sized to .313, lubed, they weigh 95 gr. consistently. Over 2.5 gr. Bullseye in Remington cases with any SP primer. Excellent performance for years.
Recently I acquired a S&W model 31-1, good shape and very smooth. My problem is: I am splitting a case every once in a while in the Smith. I marked the chambers to try and I.D. a problem chamber, all of them will split a case from time to time. I have cleaned and measured the chambers, bore is clean, but 5 groove rifling I can't measure accurately with my home tools. What diameter did S&W use in these bores, its an early 70's gun, 50 years newer than some of my Colts and 20 years newer than my newest Colt.
Does anyone have any ideas what is going on? I'm stumped, I don't want to have a special load for a problem child, I'll sell the S&W before I go that far for plinking.

No idea on what they were speced at from the factory. But I am envious as I would very much like to have the smith. I have an early police positive and like it alot, it has a very stiff trigger and the smith would be better/easier to work over.

you can mic the bullet by using shim stock around the slug and then subtract 2x the thickness of your shim stock.

OR you can see if one of the folks with the v block for measuring 5 groove will measure for you.

THROATS on most S&W 32 SWL and 32-20 revolvers I've measured run .313"-.314". Colt throats on my 32s (Bisley SAA in 32-20, Pocket Positive in 32 SWL) both run .311". Colt revolvers tend to run a bit tighter dimensions that their S&W counterparts in the same caliber.

How are you relating the split brass to the dimensions of your revolver? Are the chambers cut with excessive radial clearance? I'm more inclined to think that brass fatigue might be in play here rather than interior dimensions--unless the chambers are cut too widely.

My three S&W's handle .314" bullets well but my Ruger SP101 needs a .313" bullet as the cylinder throats are too small for .314". However, the S&W's also work quite well with .313" so that's what I run for all of them. I don't have any Colts...

Dale53

I'm with Al n this- how many reloadings have those cases had? The Colts may be cut a bit tighter, but annealing should help with the splits.

The cases have been loaded several times, but not over 5. I get 25-30 loadings from 38 Special with soft loads in Colts and S&W, Why would my 32 failures only come from the S&W??? I know when slugging the bore of a 1955 PPS in 32 it was a lot easier than the S&W and the Colt came out at .3125 and shoots very well with the .313 sized bullets. The chamber mouths are very uniform in both guns and I can push a bullet thru with minimal effort in both, leads me to believe the S&W has a "tight" bore. Guess I need to introduce myself to the machine shop up on the hill, maybe they have the tooling I need.
Thanks to all and please forward any more opinions or ideas, I like to hear from all.

5 loadings shouldn't cause splits, unless the brass lot is faulty (can happen) or the chamber dimensions are oversized. If possible, I'd run down another lot of brass--50 or so--and assemble some of your loads as listed above. Run them through the revo, and see what occurs.

One other factor to consider--a LOT of the tungsten-carbide or titanium-nitride sizer dies REALLY over-do the resizing of brass, over-working it in this process. Next comes an expander spud that opens up the case mouth for our cast boolit, and a "Coke-bottle" aspect appears in the straight-wall revolver case profile. NOT GOOD. If this is occurring during your reloading process, your tooling could be contributing to shortened case life. In the 32 SWL and 32 Magnum, I have returned to using lubed cases and a steel sizer die to avoid "Coke-bottling" hard-to-replace cases.

9.3: Yesterday I loaded 30 with 2.7 gr. of Trail Boss and 30 with my standard 2.5 Bullseye. Took the S&W and the Colt PPS and fired 15 in each gun from each batch. The Trail Boss load is lighter and slower(not chronoed, just perceived). I split 2 cases of the Bullseye load in the S&W, the Colt has never had a case failure in it.
I'm still puzzling, in fact, I'm standing here beside myself.
I'm leaning towards a tight bore in the S&W.
Nothing else to lean on out here on the prairie!!!!!!!!

I can understand the thought progression--tight bore equals raised pressures, raised pressures equals more strain on case walls. The containment of those pressures ultimately is supported by the chamber walls, so I would see what sort of dimensions I was dealing with in the S&W chambers vs. the Colt chambers. If the S&W chambers are egregiously larger than the Colt charge holes, then we have at least a partial answer. SOMETHING is causing the anomaly, we just gotta work it until the truth gets strained out.

I wish I was closer by--I'd run over with the pin gauge set and see what's up.

FWIW--I believe the D-frame Colts are a mite stronger than the I/J-frame S&Ws in 32 SWL. For all we know, some intrepid experimenter ran some warmish loads through that S&W previous to your acquisition of it. Barnes' "Cartridges of the World" once listed a load of 4.0 grains of Unique under a 98 grain bullet for the 32 SWL, and there is no way on earth I'd run such loads through either the D-Colt or I/J-Smith.

Is there any sign of sticky extraction in the S&W?

The only time its sticky is if the case has split. I've been thinking about a set of pin gauges for several years, maybe this is the push over the edge I've needed,

Have you been able to isolate the split cases to a particular chamber or chambers? A split case in a good chamber often extracts more easily, but if the swollen/split case is conforming to a swollen chamber--then tougher extraction may result.

DUH--I re-read your initial post, and all the chambers can cause it. OK, I shook my head, and my eyes came un-stuck.

Time to do some mic-ing and measuring, I'd say.

The bore on my old Smith 32 is .312 as are the throats.

To measure across the five groove slug, wrap one layer of stiff paper, or a thin feeler gauge (.001) around the boolit, then subtract twice the wrap's thickness.

I wonder if your Smith's cylinder is chambered properly or in the correct caliber? If it is chambered in .32 Colt, I would think it would split brass just like you describe. If it were mine, I'd measure the chambers of all your .32s.


Cat

Cat: it is an early 70's model 31-1. not an old gun. I have a Colt from 1909/10 chambered to shoot 32 Colt, it is a joy to use, .313 O.D. heel bullets and as accurate as any others I shoot.
No, its simply a later model S&W in 32 S&W Long, I didn't want to have a separate loading for the S&W, but I can and will until I get it measured properly.
Thanks to all for the suggestions and help. I will post a follow up some time in the future.