At least for the Smiths, I wouldn't bet that all
the barrels are 5 inches. Smith was notorious for
installing barrels an eighth or quarter inch
over or an eighth to quarter inch short. Occasionally
a sixteenth of inch variance also creeped in.
Unless SaxonPig measures all of them from the very
back edge of the forcing cones to the tippy tip front
end, I won't be a believer. He should report back.