Chuck;
Chamber dia = .463"; Bore dia = .410; Difference = .053";
.053/2 =.0265"; Co-Tan 5 = 11.43
11.43 x .0265 = .3029; Exactly what is shown on the drawing.
I definitely would "NOT" call this a Long Cone.
The cone length is shorter for the same angle in the .410 than in the larger gauges because there is less difference in chamber & bore diameters.

Ghostrider;
Normal taper for the chamber itself is about .005" per inch. The OD of the barrel at a distance from the breech equal to the chamber length is virtually always tapering more than this, so yes even moving the chamber end just " will result in a thinner wall at chamber's end. In a heavy barrel this is often of no consequence, but in a very light weight barrel can become critical.

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