| Doesn't a 68MD measure .68" in inside rim diameter. If so, that's large, if not, I don't understand the nomenclature. I'm no expert on large lips (mine are fairly thin), but I do know some very thick lipped players that use mpcs as small as .62" for lead and in the .65 to .67" range for "legit."
The .460" bore of the 1503 would make you think that it'll blow much like a ml Bach 72, but your loss of range makes me think it's blowing too free for you. Tighter backbores and/or throats will usually compensate for this.
Scurry around an find as many mpcs as you can to try to find a match. If you can't find a match, you'll never be happy with a horn that takes away that much range.
Dave |