Obviously I do not have a 28ga Lefever. To the best of my knowledge Lefever only made "Real" shotguns IE nothing smaller than 20. The L C Smith drawings did not include 28 either. I only used the 28 because that is the SAAMI drawing you posted. The subject was actually about forcing cone lengths, not bore sizes.

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