What Mouthpiece for my Besson?

[KingBassTrombone]

I've got a 1957 Besson 220 series in BBb... the goofy one with the recording bell. I've got a small fleet of mouthpieces of all sizes, but the only one I've got that fits is some Czechoslovakian mouthpiece made of German silver, I suspect for a small European-style tuba in Eb or F. It kinda-but-doesn't-really fit in the receiver and the horn is giving me plenty of hints that it doesn't fit the horn at all. The sound is very thin, gets even thinner and gritty when pushed louder... not the sound I expect from a recording bell!

My other two tuba mouthpieces are an American-shank H.N.White 26 and a Small-shank (a little bigger than bass trombone) Conn S. Neither of them fit.

So, I'm in need of a mouthpiece that will fit both this horn and my face. I'm more at home on the Trombone, and I know basically nothing about tuba mouthpieces, so I was kind of hoping the community could help a brother out. The only preferences I have is that I really like the rim size of a Conn 18 or a Helleberg, it needs to fit the Euro-shank (?) receiver, and I'd like to produce a nice fat sound almost akin to a proper B.A.T. (I know my Besson is only a 4/4... but still)

I know there's probably some multi-part mouthpiece combination that is perfect for me... but chances are, I can't afford it... so up goes the difficulty

[Heavy_Metal]

How does the Czech MP "not fit"? Too big for the receiver? Too small?

[barry grrr-ero]

The Czech's in the mail.

Sorry - couldn't stop myself.

[KingBassTrombone]

How does the Czech MP "not fit"? Too big for the receiver? Too small?

It's a bit too small. I have to wrap the shank in tape for it to fit.