The regular concert F hits in tune then falls flat very quickly. The regular low Bb hits 10 cents flat and goes down to 40 cents flat. Our students are on Schilke 51 mouthpieces but even a different mouthpiece doesn't yield any reasonable fix/change. I tried lipping the note up and I can't get it anywhere close on low Bb. Pushing a ton of air brings it up some but it shouldn't need to be loud to be close in tune.
What are your ideas for these instruments? I do have one King marching baritone that hits in tune very well but the B&H horns are a mess.
I tried a 12C, 6.5AL, and 51D with little to no change. All slides are pushed all the way in on the horn.