Fill up the mouthpiece with water, empty it into a container on the scale and weight it. The weight in grams is the volume of the mouthpiece. It’s always simple in concept.
The container used on the scale was my Waterford crystal whiskey glass. Covering the bore hole and filling the mouthpiece through the window won’t work since the side rails curve. Instead I gave the table, front, and side rails a light coating of olive oil (extra virgin) and pressed a business card onto the the mouthpiece like so:
The olive oil formed a seal and the business card lasted long enough to fill and weigh the contents five times before the card started letting water dribble through. Four of the five measurements were 24 gm while one was 23 gm. Adding one drop of water to the 23 gm measurement popped it over to 24 gm so I’m fairly confident of the measurement.
That’s 9.1 cubic centimeters bigger than what we calculated as the theoretical volume if you complete the cone made by the neck. We do have one more adjustment though . . . What do we do with the mouthpiece when we put it on the horn? Right, we put it on the neck and the amount of the neck that sticks into the bore of the mouthpiece must be subtracted out of the 24 cubic centimeters.
Since the bore is a cylinder and the cork on the neck should be filling the void between the neck proper and the mouthpiece I’m going to treat the section of neck inserted into the mouthpiece as a cylinder. When I’m in tune about 2.87 cm of neck is inserted into the mouthpiece and the bore has a radius of 0.872 cm so the volume of neck inserted into the mouthpiece is:
Subtracting this from 9.1 gives us 2.24 cubic centimeters. For you Imperial measurement fans that’s just a dash less than a half teaspoon bigger than the mouthpiece should be according to calculation.
Next: Well Fancy That