Just wanted to list in hundredths of an inch the throat sizes used in trumpet mouthpieces so you have a better understanding of what these numeric drill size numbers mean.
When you decide to have a mouthpiece opened, it is important to know how the process is being done. the correct method to open any mouthpiece would be or should be done on a lathe using a reamer (Not a drill!). Drills will always leave a swirl cut or marking in the throat section and at times drift to one side depending how well maintained the cutting edges are kept. Using a lathe and reamer will generally guarantee the opening of the throat section will be cut straight through the mouthpiece and not at an angle.
Opening the throat will accomplish three things:
1. Lessen resistance
2. Increase maximum volume level and raise your minimum volume level.
3. Reduce endurance to some degree.
Note: Increasing throat size at a certain point in each mouthpiece will start to raise the pitch in the upper range. It will also lengthen the cylindrical section in the throat section making the mouthpiece play with more slot (less flexibility). At times a backbore adjustment might be necessary to give the player the same flexibility, but most players seem to benefit from the increased slotting and centering.
If you choose to open a mouthpiece I would advise to increase the throat only one to two sizes at a time. Its very easy to have your favorite mouthpiece be turned into a paper weight.
The Brass Bow Music Co.