Quote:
Originally Posted by jefferyconnor
Here is the chamber drawing from SAAMI. Does the (20.269) indicate tolerance for the chamber?
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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.