Chamber length Win. 21
 

I measured a first year Win 21 12 gauge at 2 5/8". My 1948 LC Smith measures 2 3/4". My 1948 Ithaca is also 2 3/4". These are all unmodified guns, in my opinion, based on examination. I was surprised the 21 has the shorter chambers.

I have reviewed a lot of posts on this subject and it seems clear the consensus is that chambers cut to to 2 5/8" were intended for notional or unfurled 2 3/4" shells, as 2 3/4" shells measure about 2 1/4" before firing, maybe 1/10" longer. Do roll crimp shells vs star crimp shells affect this thought? Do roll crimp shells measure different than star crimp shells before/after firing? What was in common use in the 1930s? I have the idea star crimp plastic shells came about later. When did the makers begin cutting chambers to 2 3/4" as a routine practice? What are everyone's thoughts here?

I have 3 pre-war Win 21's, 2 20ga & a 12ga all measured at 2 5/8.

From my experience, the old paper shells were much closer to the stated length on the boxes then modern day plastic shells. Doesn't matter whether it was roll crimped or pie crimped a 2 3/4 inch shell was 2 3/4 inch when fired. All the companies, Remington, Peters, Winchester and Western introduced the "New Remington crimp," "New Peters Crimp,"

Attachment 91422

and "Super-Seal Crimp"

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on their 12-, 16- and 20-gauge Skeet and Trap loads in time for the 1939 GAH, with the new crimp appearing in their 1940 catalogs. The new crimps began appearing on hunting shells after WW-II, Remington and Peters a bit sooner than Winchester and Western.

Researcher, were roll crimp shells longer than star crimp before firing then, for the same notional length?
I've never had a chance to examine one. Well, slugs have a different crimp yet that is sort of rolled.

Yes. For some reason the manufacturers often put their rifled slugs up in slightly shorter cases. Perhaps to make the unfired length the same as a 2 3/4 inch pie crimp shell for uniformity.

Even after they went to the pie crimps for most shells, they continued to put up the 16-gauge 2 9/16 inch shells with the rolled crimp. Westerns explanation

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VERY timely thread! Yesterday I took my very early AH Fox AE grade 16 gauge chambered for 2 1/2" shells out for a round of sporting clays, using 2 different brands of 2 1/2" ammunition. The RST loads (1 oz. "Lite" in the purple cases with 'pie' crimp) measure exactly 2 1/8" unfired, while the PolyWad 'Spread-R' loads (7/8 oz. ) with rolled crimp measured exactly 2 1/2" unfired. As Researcher cites, both spent cases measured a full 2 3/4" when fired. Most interesting to me given the differential in actual measurements of the cases vs. the chamber labeling on the box, both at 2 1/2".

I found that modern black case Remington 2 3/4" shells only unfurl to about 2 9/16" Other brands pretty much go 2 3/4". I reluctantly shot that in my 2 1/2" 16 until I got onto RST.

I shoot the black Remingtons in every 16 I own except short chamber Model 12s, which won't feed them. I haven't blown one up yet.

In his definitive book "Winchester's Finest - The Model 21" author Ned Schwing states on page 96 that all 21's in 12-16-20 gauge were chambered 2-3/4" from the very start of production, except for 28-gauge initially 2-7/8" and then 2-3/4" after the War. That excludes of course those factory chambered and stamped 3-inch.

Some additional comments: often modern "gauges" that depend on seating in the taper of the chamber and correlating to its length can give inaccurate readings owing to their manufacturing tolerances and/or chambers cut with reamers that were worn or with an inaccurately ground taper. Also, gauges that bump into the start of the forcing cone can give inaccurate length measurement unless sized exactly to period SAAMI front chamber diameter and even then you've got a +/- tolerance on diameter. A few thou in diameter makes a big difference when trying to measure length. Then you have the budget techniques using cut-off shells, dowels, machinist scales and rolled up postcards. Best ime for those that fret chamber length, shell overlap into the cone, etc is a gauge that's accurately made on the lathe between centers and sized dead nuts to absolute minimum of that SAAMI front chamber diameter. With such gauges I've measured every 12 and 16 Model 21 I've ever owned including Prewars and found all to be on size or a tad longer than 2-3/4" or 3" if stamped for 3-inch shells.

Top 10 and 12, Bottom 20 and 16
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Thanks for commenting on the post, Cold Spring. Those are nice gauges you have! I've been using a Galazon brass leaf gauge. It only measured .780", I put tape on the edge to bring it up to .798". My measurements do seem repeatable, at least. I mainly use it to see if a chamber has been lengthened from factory. I never had gauged this three digit 21 before and I only own one other 1940 made 21, it's at my ffl's shop, as I'm selling it and I never measured it. My assumption about this 21 is that it for sure was a 2 3/4" cut chamber. You could have knocked me over with a feather when it gauged 2 5/8". Measuring a couple other guns of mine that are handy with my shabby gauge: a post-war LC Smith gauges 2 3/4", as expected and a 1925 Parker gauges 2 5/8", as expected. I'd like to get a more accurate gauge, do you have a recommendation of which commercial one might be okay? Do you happen to know SAAMI chamber end diameter in 1931? Their website shows .798" currently. Any other thoughts where my error might be coming from?