Please note the .774" dia gage I mentioned earlier is "Not" for a chamber length gage. Most current specs seem to call for .798" as the minimum dia for forward end of chamber. A drawing from the 1950's era by noted Gunsmith Roy Dunlap cited chamber specs for 12ga 2 3/4". Minimum chamber called for the .798" dia to occur at min length of 2.614" from breech & with a 5° forcing cone. The .774" was a "Mathamatical Calculattion" of the dia of the "Forcing Cone" in a gun having this minimum chamber at 2.750 from breech. I suggested it might well be useful to have a gage of this dia to & to insure it would go into a bbl to at least the length of the fired length of shells one was contemplating using. This would catch those chambers having very short, steep cones which should likely "Not" be fired with shells longer than actual chamber depth. This gage would thus be used in "Conjuction With" a chamber gage, not as a chamber gage itself. I generally check chamber depth (even though I turned a set of 12, 16 & 20 on the lathe) with a 6" machinist scale. From my limited experience in this it seems the "Tight" chambers are more prevelent on older American & Continental guns than on English ones. This is the reason though I usually just use the scale.
I tried the 20 in a 12 & to me it seemed useless as the 20ga rims I checked were .760" or less.
