Chamber diameter

[spyder]

What is the typical chamber diameter for a Philly 12g. Thanks.

[spyder]

Well no responses yet. I am trying to make a chamber length gauge. I read where the modern standard chamber for a 12g is .798. I can start there and fiddle with it. Right now, I drop a 3.5" shell in and see where it stops, but I know it's not quite accurate as a small portion of the shell fits into the cone.

[jolly bill]

Spyder,

A cheap and dirty chamber gauge can be easily made with an empty, fired plastic shell.

Cut the empty hull squarely in two right at the junction of the plastic body and the brass/steel base. Clean up the cut plastic part. Measure it for length and insert the squared off cut part in the chamber til it stops at the forcing gun. With a steel scale, just measure how far in the chamber your gauge is and add it to the length of the shell you just cut off.

Works fine. Make one for all gauges if needed.

Did I say cheap and dirty?

Jolly

[spyder]

JB. I should have searched before I posted. I see your instructional post from a few months ago. Thanks for the help.

[Researcher]

Chamber depth is considered to be the distance between the breech end of the barrels and the joint between the chamber body itself and the forcing cone, which reduces down to bore diameter. This is loosely based on the length of the "Fired" shell. Today, theoretically when the crimp opens on the shell being fired the end would land at the junction of the chamber and cone. Prior to WW-II many companies had the practice of holding the chamber about 1/8 inch shorter than the shell for which it was intended. Fly in the ointment is nominal measurements often differ from actual ones in both chambers and shells. A very good method I have found of measuring chambers without much outlay of cash, and is quite accurate enough for virtually any situation, is a common 6" flexible machinist's scale which you likely have. Hold the barrels with muzzles toward a light source, not necessarily a concentrated one a window is great, while looking into the breech and the cone will be thrown in a shadow. May have to move the barrels around a little until it is distinct. While still looking into the chamber simply slide the scale in until you observe the end coming flush with the shadow line & mark position of breech end with your thumb. Remove and read the scale. I usually repeat this a few times to insure I am getting a consistent reading, but you will be amazed how accurate this can be done. While I own a Galazan chamber gauge, I use this more often than not. The chamber body itself has a taper of about .005" per inch. Sometimes chambers were cut with slightly worn reamers giving a slight undersize chamber. If the chamber is a bit undersize a gauge made to "industry" standards will not go in to the true depth of the chamber. A.H. Fox Gun Co. shotguns are known for having tight chambers. The machinist’s scale method can be more accurate.

Here are all the measurements according to Ithaca Gun Co. --



According to the late Austin Hogan's measurements of the chambers of BoWhoop, they were .788" at a depth of 2 7/8 inches, a lot tighter than the Ithaca specs.