Chamber length Win. 21

[jefferyconnor]

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?

[James L. Martin]

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

[Dave Noreen]

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,"

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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.

[jefferyconnor]

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.

[Dave Noreen]

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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[Kevin McCormack]

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".

[jefferyconnor]

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.

[Bill Murphy]

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.

[Frank Srebro]

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
.

[jefferyconnor]

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?

[James L. Martin]

I used a Galazan chamber gage pictured and a 6 inch ruler ,both came up with 2.658 pretty close to 5/8 which is .625. I have no idea how accurate the gage is or my method with a 6 inch ruler.

[jefferyconnor]

Here is the chamber drawing from SAAMI. Does the (20.269) indicate tolerance for the chamber?

[James L. Martin]

Well just measured my gage and it's .796 that's. 002 smaller so it would go in deeper and give a very slightly deeper reading if anything. So I must say either my chamber is tight and giving a false reading or my chamber is 2 5/8. I also measured the markings on the gage for 2 3/4 and they are correct. The Win 21 is a early one # 1761.

[Frank Srebro]

Here is the chamber drawing from SAAMI. Does the (20.269) indicate tolerance for the chamber?

No, the 20.269 shows the .798" diameter converted to millimeters.

The diameter tolerance is shown in the small rectangle = +.005". Thus .798" is the minimum front chamber diameter on that drawing which seems to be a current one. The length tolerance is also indicated as +.050". Please remember the guns we're interested in were chambered by men turning dials and without digital readouts, also the reamers were ground on relatively primitive machine tools as compared with modern technology, and said chamber reamers were used until worn undersized as reckoned by the workmen.

Sorry I don't know of a commercial source for precision chamber length gauges that butt into the very start of the forcing cone. Some years ago I bought a set from a well known gunsmithing supply place. They were made of steel and oversized at the business end. I sent them back and had mine made at a friend’s machine shop. The material is 2024 aluminum shafting and I had 5 extra sets done up for friends and at cost, something like $65. per set as I recall. All are long gone but anyone with access and ability on a precision metal lathe can do the same. Also there are machine shops most everywhere and you can likely get one or more made up with a simple drawing.

My 10/12 gauge in the pic has rings cut at 2-7/8 and 3-1/2" for 10-gauge, and at 2-1/2, 2-3/4 and 3" for 12. The 20/16 are at 2-1/2, 2-3/4 and 3" for 20-gauge, and at 2-1/2 and 2-3/4" for 16.

[jefferyconnor]

Wow, okay so based on those tolerances length can currently vary by a .100" and diameter by .010" at the extremes. When gauging a chamber, especially with an double ogive like Parkers had or a shallow forcing cone it seems it would be easy to get a false long reading to the start of the forcing cone. I've carefully remeasured a couple chambers and in one case a chamber I thought was 3" was actually 2 7/8". My Winchester 21 stubbornly continues to measure at 2 5/8" and I seem to be feeling a definite stop. Yet the chamber could be undersized by modern standards at the end of the chamber. I'll see what it gauges with a .793" min. gauge.

[Frank Srebro]

You are misreading the tolerances in the rectangle on your print. They are +.005” and +.050” respectively. Not minus (-). Hence the diameters and length measurement shown on the print are the respective minimums.

[jefferyconnor]

You are misreading the tolerances in the rectangle on your print. They are +.005” and +.050” respectively. Not minus (-). Hence the diameters and length measurement shown on the print are the respective minimums.

Thanks! This thread has made me realize measuring chamber length accurately is harder than I thought, most people want to know the length to the juncture of the forcing cone, so do you think a .798" pin type gauge would maybe be the most correct and accurate?

[Frank Srebro]

I'd say it depends on Winchester's chamber specifications when your 21 was made. Earlier on, makers were using their own 2-3/4" specs. For example some Foxes were made with tight chambers though on size as regards length. There's no date on that print you posted but you said it's current SAAMI for 12-gauge 2-3/4" and presumably you are or will be shooting modern shells. Hence a .798" diameter pin gauge should let you verify your gun(s) chamber length relative to that print.

Yes this has gotten too involved. My last reply here.

[Bill Murphy]

The beginning of a forcing cone is a visual sighting at the end of a machinist's scale. An alternative is the movement of a dial on the end of a choke gauge. The actual dimensions are rather irrelevant as long as your loads are safe.