As I recall the Ferguson story in SSM the ends of his chambers were essentially a step rather than a cone. This was allowing the ends of the fired shells to actually unfold into the bore itself. SAAMI Specs on 12 gauge chambers for 2 3/4" shells for many years specified a minimum length of 2.6136" with a maximum of 5° (10° included) taper from a minimum diameter of .798". Max fired case was listed @ 2.760". A max length hull in a minimum chamber would thuis lap into the cone by a length of .1464. Cone diameter at this point would thus be .772" or .026" smaller than the chamber end. This amount can well be tolerated. The end of the hull lapping into the bore proper is a "VERY BAD" idea as Mr Ferguson found out. He was fortunate indeed that nothing more occurred than cutting off the ends of the hulls, it could well have been a lot more dramatical.
Moral, on an old gun always check out the chamber to see exactly what it does have. A simple look down the bores from the breech would have revealed that sharp step as opposed to a tapered cone, giving forewarning not to use a hull which was longer than the chamber..
I don't recall the particulars on make & age of Mr Ferguson's guns, but I would be Extremely surprised if one as late as the 1930's had this type of chamber. Not many even from the 1890's would have. This is more something one would expect to possibly encounter in a "Very Early" breech loader.
Last edited by 2-piper; 11/20/16 04:58 PM. Reason: mistake corrected
