Chamber length Win. 21

[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.

[jeffery c]

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.

[Cold Spring]

Originally Posted by jefferyconnor

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.

[jeffery c]

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.

[Cold Spring]

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.

[jeffery c]

Originally Posted by 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.

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?

[Cold Spring]

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.