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

I too have the Skeets Bore mic and found the same issue with it. Then I purchased several "chamber gauges" all of which gave me varying chamber lengths. I'll use the one(s) with rim diameters of .797-.800.

Jim,

I don't recall who made various friend's bore mikes, but, they nicely captured chamber profiles, forcing cones and bores, for 12 and 16s. Think they all had permanently attached heads, but, I really did not pay much attention to anything but the measurements.

Niklas

Might be that a telescoping bore ["T"] gauge could be set and locked at the chamber end measurement with a caliper. Cheap ones I have will at least reach three inches. Measurement of depth at beginning cone would have to be from centreline of the T bar along the handle as the contact is domed.

jack

I recently came across this 1906 English chart.


Pete

Not of much concern to many of us, but a "True" 4 gauge bore is 1.052". The dimensions as supplied in this chart are for the more commonly used paper cased load. While the gun (if marked for gauge) & the shells would have been sold as 4 gauge, @ .935" for bore the proof house would have stamped the bbls with a "6" (.919"). They would have had to accept a .938" plug gauge to be marked even as a 6/1.
It is noted that from 10gauge down through 24 gauge the front of chamber (point B) is about .070" larger than bore dia. Below 24 gauge this difference is slightly less, while the 8 gauge is about .080" & the 4 gauge a full .100". Yet, with a "B" dia of 1.035" the forward end of a 4 gauge chamber is still .017" smaller than the true 4 ga diameter.

PS;
I normally measure the depth of my chambers with a thin ½" wide x 6" Starrett machinist scale. A "General" from your local home improvement store will serve the same purpose, but as a former machinist I had the Starrett.

If the chamber had been lengthened here in the UK it does not have to be reproofed by law.Don't ask me why?
A few years ago it became fashionable to lengthen forcing cones to reduce recoil and enhance patterns.Every gung ho gunsmith bought a Clymer reamer and had at it.
I never bothered, just carried on polishing wood.
Now it seems no-one else bothers?????
Fashion??
I am still waiting for Drapes & Crepes to come back into fashion, unfortunately the quiff went longtime ago.

This thread got me curious, so I checked the chambers on my A.J. Aubrey and American Gun Co. shotguns, thinking for sure they would be 2 9/16" chambers. But when measured with my telescoping guages and micrometers, both are 0.798-0.800 at 2 3/4" from the face of the chambers. I guess then that I can assume that both have been rechambered to 2 3/4" and should be ok with standard 2 3/4" shells? I reload with very light loads btw.

Oscar;
One would normally assume the term "standard 2 3/4" shells" to mean factory SAAMI spec loads, for which this gun should "NOT" be considered OK. I assume here you are really meaning the standard 2 3/4" hull length as loaded with low pressure reloads. This is a totally different thing. I do not believe the 2 9/16" (65mm) was ever a standard 12ga (It was standard in 16ga) length in the US. Much more common was the 2 5/8" (67mm) length. Also 2 3/4" lengths were readily available much earlier than many seem to be aware of, so it is not correct to automatically assume a gun having 2 3/4" chambers has been re-chambered. There may simply be no way to prove it either way. Often about the only thing one can do is just to insure there is ample wall thickness at the end of the chambers.

Salopian:
You said:

"If the chamber had been lengthened here in the UK it does not have to be reproofed by law."

Is this really true? I have always assumed from what I heard on this BB that any lengthening of a gun's chambers AUTOMATICALLY required it to be reproofed before it could be sold legally.

I would probably be tough to determine where the gunsmith did the work.

To all:
I would be using low-pressure loads in any case.