Nice looking picture, however I am of course totally unable to "See" the dimensions of the chamber which are inside the barrels.
I will still have to say I have yet to see a shotgun which did not have somewhere close to that .005" of taper per inch of chamber length. This was established very early on as quite essential to aid the extraction & of course later the ejection of the empty hull.

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