A friend has a Conn 90G marching trombone with 0.547 bore:ThomasDodd wrote: The O-21 was the marching trombone from Olds and it had a 0.500 bore, as did the O-20 valve trombone. Now, if I took either of those horns and wrapped it like a bell front euphonium/baritone, would that be closer to a euphonium or a British baritione?

It's a lot skinnier than his Besson English baritone and the tone doesn't resemble the baritone very much either. It also has some interesting intonation issues.