Yeah, if they are Bach mouthpieces the inside rim diameter sizes are as follows:
The 2 series 16.50mm
The 3 series 16.30 mm
The 7C is the smallest at 16.20 mm
The C cups are medium and the B cups are medium deep
I always found the 7 to be a cookie cutter ( sharp rim ). The 3 not too bad for comfort, but the 5 size ( 16.25 ) always worked best for me.
NOTE: the deeper cups are more tiring on the lips, bad news if you want to build range.
Spend some time on long tone exercises, especially whole notes. They help you develop good breathing and a smooth tone...and even endurance. The next important thing is working on scales. Start with a one octave C scale ( C below the staff to mid C on the staff ) and slowly over time work your way up a second octave until that great day when you discover you can play a HIGH C ABOVE THE STAFF.
Hope this helps,
George