doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Chamber Gauge

Hi all, just curious, are these accurate:

http://www.csmcspecials.com/Handy_Model_Chamber_Length_Gauge_p/t0320.htm

If so, does anyone have one they want to sell?

Thanks!

Greg

I've used one for years and they work just fine! Well worth the $39.

I use these tools.





You measure the length of the chamber by sliding it in to the chamber spread so there�s a slight drag. When you get to the forcing cone it�ll stop, then I mark the shaft with a sharpie pen and measure it.



You can also use it to measure interior bore diameters.

Steve

Yes, the Galazan/CSMC Chamber Gauge works just fine. Quick and easy, you won't regret buying one. Use mine quite often, especially at gun shows.
JR

The blade type gauges and the plug type both work well for standard chambers, but neither will correctly measure a chamber that is over or under size. As an example, I have two Tobin doubles that check out at 2 1/2" with a Brownell's plug gauge, but proved to be 2 3/4" when checked with Rock Doc's system. Only a difference in diameter of 0.002" is enough to throw the measurement off considerably, but would have no effect on the chambering and firing of standard shells.

I got the Galazan/CSMC gauge as a gift at the NRA breakfast in conjunction with the Gold Medal Concourse, and it is fine in a perfect industry standard chamber. more often then not I use a plain 6-inch machinist scale.

I've also used the Galazan gauge for years, and I can't recall that it's gotten me into trouble. My understanding is that in 12ga, standard British chamber diameter is .800; .797 is standard American. Just ran it into my 2 1/2" Lancaster. It may go a hair or 2 beyond the 2 1/2" mark on the Galazan gauge, but not much more than that. And it very clearly isn't 2 3/4". I think the taper of the forcing cone saves you from being led astray, at least insofar as reading short chambers as longer ones. Longer ones as shorter, in the case of the Tobins above . . . interesting. Don't think I've ever encountered undersize chambers. It would seem that that might cause a problem when it comes to chambering shells.

Difference from the diameter at chamber end of a standard chamber to a bore of nominal diameter is about .070". Thus the cone tapers down by that .070" over its length. The chamber body itself has a nominal taper of about .005" per inch (can be slightly less) so a 2�" chamber has a taper of .0125" over its length, a 2 3/4" chamber has .01375" & a 3" chamber .015" of taper. On any of these if you insert two plugs having a difference in dia of .001", assuming both fall between the small & large dis's of the taper they will stop .200" apart.
As can be seen there is little likelyhood of reading a short chamber to be a longer one as Larry stated. There is indeed a great likelyhood of reading a chamber to be short when it is in reality only a thousandths or so undersize. This will present a problem in chambering "Only" in the case of a shell measuring right on maximum. I have never encountered any modern hulls which do, in fact most run well below maximum. I have had several guns over the years that a chamber gage built to minimum chamber dia would show to be short when they in fact were not, only small. Never had a problem with a single one of them chambering a shell. These guns were pre SAAMI guns, which of course are also the ones with un-marked chamber lengths.

Problem in measuring with rules and calipers is that if the chambers or the cones are pitted then you can not get a very accurate reading . Do not also forget that under pre 1984 British poof there was a 100thou" plus tolerance [ don't have the exact figure to hand] effectively making the chamber 2&5/8" at is maximum depth .

So......if I reading and summarizing correctly, you can only be sure that a chamber length is about 2 1/2", 2 3/4", etc. because of the possibility of under or over sized chambers in our favorite old guns.