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Would someone tell me how to measure the length of the chambers in my 12b. The proof marks preceeded such niceties. I've been trying,but each measurement conflicts with the previous.
thanks
Justin

An internal spring caliper works very well, simply slide it down the chamber with a little spring tension on it. When it stops you've reached the end of the chamber. Next carefully mark with a felt tip where it protrudes even with the chamber opening. Finally screw the spring tension adjustment screw in slightly to remove spring tension and remove from the chamber. Measure the distance from the caliper end and the felt tip mark with a ruler for your chamber length.
One added bonus, one internal spring caliper can measure many different sized chambers, you can also use it, combined with a micrometer to measure choke and bore sizes.
Steve

thanks,Rockdoc. Internal spring caliper? please direct me towards one,preferrably an inexpensive one.
Justin

Justin, there are lots of ways to measure chambers that don't require engineering tools. Simplest is to spend $39 with Galazon online and buy a brass multi-guage chamber guage. Just poke the appropriate guage into the chamber till it stops and read the chamber length. Next simplest is to run a little steel ruler into the chamber while holding the barrels up to a light source, stop at the 'shadow' where the forcing cone starts and read the length...Geo

The traditional way to do this is with a chamber gauge which is slug of steel, brass or whatever machined to the correct measurements for the muzzle end of the chamber and marked off at the appropriate distances along its length. Given the correct measurement for the gauge of gun that you want to measure, any half competent engineer with a lathe could knock you out one in about 10 minuted.
Alternatively, you can buy one from Brownells for a few $'s.
Only flaw in this simple scheme is if your chamber is over- or under size in diameter in which case you will get a false reading of depth. For example, I was measuring a gun that had had the chambers dropped yesterday and although with bore gauge I could see it had 2 3/4" chambers, the chamber gauge gave me less than 2 1/2"!

Geo
Engineering tool! I'm just a simple geologist, not an engineer. You can purchase a inside spring caliper at Home Depot for $10 or less, here's some examples http://www1.mscdirect.com/CGI/GSDRVSM?PMTYPE=&SITEXT=SPRING%20CALIPER . Yes if you want to use the tool for measuring inside diameters you'll need a micrometer or vernier caliper to measure the spread of the spring caliper, here's some more examples http://www.tresnainstrument.com/vernier_calipers.html but even those items can be cheaply obtained.
Steve

I have a set of turned brass gauges I use in the shop. For portable use the best I think is an inside dial caliper like the one below. You can see exactly where the forcing cones start it also will work as a quick choke measuring tool. Its leg length is 3.25" and will measure from .375 to 1". I bought mine 20 years ago when they were cheap, Enco has them for around 80.00, you might find on on ebay for a lot less.

Jim

A reliable "field expedient" if you will: Take a fired 12 gauge shell. Reverse and insert a 12 Ga wad into shell until base of wad is even with mouth of shell. Insert this into chamber until it meets resistance. Mark and measure.

The Chamber Length Gauge from Galazan's works well for me, no fuss no muss. If you're going to be messing with doubles you might as will get this, the choke gauge and a good wall thickness gauge. Don't cheap out. IMO

Tim

RocDoc, you have no idea the depths of my fear of advanced machinery; the very word 'caliper' conjers up visions of vastly complicated things to me...Geo