I have a trumpet mouthpiece schilke 13A4a with a shallow cup "A" and a tighter backbore "a".
Recently I saw from the internet a music store selling a mouthpiece model schilke 13A4. The
store describes this model as same as the model 13A4a but with a backbore size "c" making it a freer blowing mouthpiece.

The term "freer blowing" is used in describing a mouthpiece, may also be a technical term with some other meanings. Does this mean that you must use more air to blow the trumpet??

Pls. explain further this term, and the other effect of backbore size "c" on the trumpet. Can you compare it to the 13A4a model??

thank you .