I have played a Besson 700-series intermediate horn for about 15 years, and decided to make the leap into a pro-level horn. I got a pretty good deal on a relatively new Besson Sovereign 967, but I'm having problems with the lead-pipe or receiver.
Both my horns are large bore and I have 2 Schilke mouthpieces and a Bach mouth piece and have tried them in an older 967 that belongs to a colleague and they fit properly. All three fit my 700-series properly, as well.
But in my 967, it's as though the tip of the shanks (this problem occurs with all three of my mouthpieces) are interfered with by the venturi so that the mouthpieces stick out of the horn about a 3/8" farther than on the other horns. The three problems this is causing me is that I have to push the main tuning slide in somewhat farther, sometimes all the way; the mouthpiece shank doesn't seat completely at the rim of the receiver (it's not very obvious to see unless you're looking for it. It appears from just a few feet away to be seated, but it isn't -- you can 'rock' the mouthpiece back and forth ever so slightly like a 'loose tooth.' When doing this you can see a bead of fluid being pinched out between the shank and the receiver rim); and finally, the mouthpiece is prone to dropping out of the receiver.
I called Besson, and kinda got an "anything before 2006 isn't our problem" attitude, however I wasn't demanding any warranty-repair work. I had hoped they might be open to letting me pay them to replace the lead-pipe and/or receiver, but I got the feeling that they aren't interested.
The suggestions Besson made was to replace the receiver, or replace the lead-pipe/receiver assembly. I asked about modifying the mouthpiece shanks and he mentioned that it could mess up the horn's intonation.
I called the repair shop that I bought the horn at and they suggested first trying to de-solder, move out (making nominal horn length longer) and re-soldering it so the distance between the receiver rim and the venturi is increased.
Now I've been playing Euph since I was in High School, and I'm well into my middle ages now. I keep hearing references to the 'intonation of the horn' and elaborate tuning setups, but I've never fully understood what all this means. I just adjust the main slide until the open overtone series is in-tune, and then pull out the 1st slide just a touch so the middle "G" is correct. I have just lipped everything else to the correct place and I never get complaints from anyone about intonation. Because of this, I'm not sure what way the intonation of the horn can be affected such that a main tuning slide adjustment can't correct it. I suppose if I have to push-in all the way on the main after the receiver is moved (if I go that route), that I could have the main tuning loop chopped to compensate.
I'm not sure which way to go with the repair, and what the ramification of these options are.