Chuck;
Sorry to Burst your Bubble;
Using diameters of .614" & .545" connected by a cone having A 5 ANGLE from bore axis per the SAAMI drawing I come up with a length of .394336804".
Now you might like to work with a bit more precision than that, but that's as many decimal places as my little Casio calculator will work to. Plenty close enough for a TN Hillbilly. That is not as long a cone as Drew's chamber cast of a 1905 Smith shows nor what 1907 & 1935 Smith drawings show. I have not actually measured the cone length on any of my Lefevers but I can assure you they are no shorter than that.
That SAMI Spec cone is "Modern" only if you compare it to one of the rare very early guns with the chamber ending in an abrupt step rather than a cone at all. Even my pre 1865 W & C Scott pinfire has a cone & not a step.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra