A friend (who has been playing bass saxophone professionally for three decades) and I (who just recently acquired mine) both experience very low tuning (top of left hand) and somewhat low tuning (bottom of right hand) with our 101-year-old (serial numbers within a couple hundred numbers of each other) Buescher bass saxophones.
Anyone who chooses to is - of course - free to respond with suppositions/criticisms re: what about... leaks, pad height, mouthpiece (mine is the o.e.m. Buescher-stamped mouthpiece in mint condition), embouchure, reed, "low pitch", "you're not doing it right", "says who/says you", and whatever, but I've already tested a very rough mock-up neck (which completely solved the problem) and - today - I went ahead and fabricated the first (of two - one for me, and one for my friend) "final version" shorter neck tube. (This wasn't particularly easy for me to fabricate, as (though 45 years at it) I'm a repair-guy (not an instrument-maker), and (obviously) don't have - LOL - a "bass saxophone neck mold" (nor hydraulic puller) laying around waiting to be of use. (again: Anyone is absolutely welcome to criticize this tack, but I won't be offering any rebuttals...When a woodwind instrument plays generally quite flat at the top and somewhat flat at the bottom - the capillary portion of the instrument is obviously too long (particularly when - simply - shortening that portion of any instrument completely eliminates the issue, and - those whose same-make instruments don't feature this same issue - I'm truly very happy for you...but my instrument - and my friend's - have been problematic, and this will fix the problem with both of them.)
Sometime in the next few days (because I have customer work to do - which pays the bills) some copies of my original male connector (temporarily removed from the o.e.m. neck tube - as seen) will be fabricated on the lathe...I've already ordered and received the 30mm diameter cylindrical chunk of brass required to make those.
This should define my friend's playing (sans epic lipping and working very hard to do a good job with good tuning) as far easier and more pleasurable, as well as my own playing being defined as considerably more pleasurable from the very beginning of my own bass saxophone journey.