GR has seen that many players are confused regarding equipment mismatches and rightly so. There are no standards in the industry and even if there were, many times there are errors in manufacturing. So, here goes from GR. The quotes you see are from a thread on The Trumpet Herald:
Nkolisnyk wrote: “They don't bottom out and appear the same length (which may be hard to measure between brands - for example in the cornet world, Wick 4B's are much shorter than Curry 3BBC)
This is a good statement. Shank length has nothing to do with bottoming out or a poor fit. Short or long overall length mouthpiece it doesn’t matter regarding the receiver. The mouthpiece taper shank lives in the receiver taper and that is the mating area. Beginning taper diameter is the key. At GR we make trumpet shanks from a beginning taper dimension of .375 for a few really old horns to .395” for players that have a worn receiver or had the misfortune to overuse a $29 reamer off the internet.
The old Bach printed material stated a beginning dimension of .382” with 1” engagement and a taper of .050” per inch or 50mm per1 meter. That was used for years by Bach and Schilke. From my measuring Schilke may use this dimension of .382” today and match it to their receivers. You can call them to verify.
In 1999, GR called some of the major manufactures to start a Manufacturing Organizations for the purpose of setting standards like the auto industry (SAE) and others. One laughed at him….GR said are you laughing because you don’t have a tolerance or your process can’t hold the tolerance….the engineer laughed harder. Your answer, you must chase the manufactures tolerances or quality in order to get a good match.
Note every .001” on the shank diameter and the gap or engagement will vary .02”.
Let’s say you have a dialed in CNC machine to make the shank of the blank that will hold +/- .0001”. You have it right? Not so fast! Next in the process is your polishing. The mouthpiece buffer is feeling strong and there are some machining likes they want to remove….ok the takes off .002” on one .003” or more. The next buffer only takes off .001” what do you have? You have a variation of .003” or more to be kind or a change in gap of .06” about 1/16th of an inch between parts. You are scratching your head yet? Ok we introduce plating. Some platers will put on .0002” or 200 micro inches of silver for a total shank increase of .0004”, your tolerance stack up could put you pretty darn close to the target dimension or .0025 to .003” small. There are other platers that put on .002 to .004” of Silver for a total dimension change of .006” or more adding .120” plus to the gap. Holy Bat measuring this is becoming a nightmare. Oh, now add the tolerance stack up with the receiver and you have introduced even more, not to mention wear with age, and the guy the likes to tinker with a receiver reamer for those of you buying used horns.
If your mouthpiece bottoms out. Don’t cut the shank! Stop, and figure out what is going on. Measure shank and receiver, do it several times and take an average. If your numbers don’t repeat send it to someone like Charlie Melk. If you are not qualified stop and get help before your make a mistake or remove metal you can’t put back. Often these fixes are not real complicated for a repair person that is prepared to deal with them.
Measuring the shank. It’s pretty hard to do with a digital calipers because the end of the shank is often rounded or it could have a dent.
One way to get a good fit on an older mouthpiece is to have Plating added to the shank OD only. It you add too much it can be carefully buffed to proper fit.
Nkolisnyk wrote: “It's like the tip of the shank is slightly wider on the Bachs than they are on the Yamahas. If I give the Bach a little twist, it snugs in (but I don't like doing that - I feel it will hurt the receiver over time). Interestingly, my Curry 3C. does the same thing (though to a lesser degree) but it fits just fine in my Bach Strad.”
We have seen this condition. Often from buffing or putting something down the backbore that has flared the end of the shank. The shank may have had a dent in manufacturing and they flared it removing the dent. It would be slightly bell mouthed and would rattle. Mouthpiece and receiver fit is the biggest area of mismatch we see today.