Bach 5C vs Marcinkiewicz 310
The Marcinkiewicz 310 has a wider cup diameter, the Marcinkiewicz 310 features a deeper cup.
Cup Diameter
The Marcinkiewicz 310 has a cup diameter of 17.20 mm / 0.6772 in compared to 16.25 mm / 0.6398 in on the Bach 5C — a difference of 0.95 mm / 0.0374 in. A wider cup generally produces a fuller, darker tone but requires more air support.
Cup Depth
The Marcinkiewicz 310 has a deep cup while the Bach 5C has a medium cup. Deeper cups favor a darker, richer sound; shallower cups provide more brightness and easier upper register.
Throat Diameter
Throat diameters are essentially identical at 3.66 mm / 0.1441 in, so resistance feel will be comparable.
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.