doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com "Measuring" chamber length

Thank you thank you thank you!

I was the one that made the .774 guage, lacking any other dimensions to use.

It is not a big deal to make one, but the info on the sizes was not easily found online.

It will shortly be replaced with something a bit closer to the specs here.:)


Cheers
Trev

That is some gauge, that would show a 3" chamber to be 1/2" short at the 3" mark. Are you sure of that 3.505 measurement on the Brownell gauge?

Interesting stuff indeed!
So it would appear that a gauge with a rim diameter of .800" should fit into the gun's chambers to a depth of 2 1/2" (from the breach face) for a gun proofed at 2 1/2". If it goes to a depth of 2 2/4", the gun's chambers were likely let out to accomodate longer shells, thereby remdering the gun out of proof. Correct?
Could there be any other inferences made?

8bore,

I just checked it again, with my dial indicators, and it shows 3.505, that's 3 1/2" + .005. When I first checked it, I thought it to be a little obtuse, but I am giving you what the dial indicator says. The needle is showing .005 past the little 5 after the 3" mark on the sliding scale. Now, if I am in error, please correct my ignorance!

humbly I am,
binko

This has been suggested befo', as BHO says, but I'll repeat it here. A lathe is cetainly not necessary to make a chamber gauge or set of gauges. I bought a half dozen stainless steel rulers at a yard sale, several years ago. By narrowing the ruler to the width you want, for 3-4", you will have a very inexpensive chamber gauge. The same could be made out of brass or aluminum flat stock but the rulers have the advantage of having the numbers on them already. you insert the gauge as far as it will go, read the numbers at the breech end of the barrel(s). It will stop at the beginning of the forcing cone(end of the chamber). The number you see is the chamber length.

Diameter "C" is as follows: 10 ga. .845", 12 ga. .800", 16 ga. .732", 20 ga. .685", 28 ga. .614", 67 ga.(.410) .465"

I have a sheet showing all the pictured dimensions for 4 ga. through "No. 3". Send me your e-mail address(shown in my profile) and I will be happy to scan it to you. Don't waste your time or mine with PM's. E-mail me directly.

Re Mr. M Grubers earlier comments.
Yes your analysis would be correct but not all encompassing.
If the chamber were let out here in the US it would almost certainly have been done with a commercially available reamer ground to SAAMI spec of .797" thus your 800" would still stop at 2&1/2 ". you would need to visually check for a very minor step.
I find it useful to have a plug at .796" to double check for this condition.

Okay makes sense.
I would assume that if it was done in the UK, it would have been sent for re-proof.

Only two totally reliable means of measuring length I know of are the system that Jim Legg describes above and a proper (bore micrometer) bore gauge with ruler. When using the system Jim Legg describes, I also use a good light to verify that the end of ruler is actually stopping at start of forcing cone. After finding that some of my old European hammer doubles have chambers that standard American chamber gauges show as 60 or less mm, I ONLY trust these two methods of measuring chamber lengths.

Niklas

I have a Skeets Bore mic but the 12 ga. head doesn't go large enough to detect the end of the 12 ga. chamber. It goes into the FC about 1/4".