Bob Reeves 40/B/X vs Kelly 3C
The Kelly 3C has a wider cup diameter.
Mouthpiece A
Bob Reeves 40/B/X
• Cornet
Cup diameter15.88 mm / 0.6252 in
Cup depthVery deep
Rim width—
Throat diameter—
BackboreX
Finish—
Material—
vs
Mouthpiece B
Kelly 3C
• Cornet
GeneralCup diameter17.02 mm / 0.6701 in
Cup depthVery deep
Rim width—
Throat diameter4.06 mm / 0.1598 in
BackboreL
Finish—
MaterialLexan polycarbonate
Best suited for
Orchestral playing — large cup for full, dark tone
High-volume projection — open throat for power
All-purpose mid-range
Cup Diameter
The Kelly 3C has a cup diameter of 17.02 mm / 0.6701 in compared to 15.88 mm / 0.6252 in on the Bob Reeves 40/B/X — a difference of 1.14 mm / 0.0449 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
Both mouthpieces share a very deep cup depth, so the sound character from depth alone will be very similar.
Material
The Bob Reeves 40/B/X is described as unspecified, and the Kelly 3C as Lexan polycarbonate. Material affects mass, warmth, and how quickly the piece responds.
Which is better?
Neither mouthpiece clearly dominates the other — the right choice depends on your embouchure, playing style, and the sound you're after. Try both if possible.