There is an interesting series of notes in the commentary to the Schottenstein Edition of Nedarim vol. I (37b3) concerning matters of vocalization and cantillation.
Note 27 discusses the function of the matres lectiones, the Hebrew consonants which double as long vowels (א, ה, ו, י). An example given is how a ו shows the חולם is to be pronounced in a word (חוֹלָם; with an"o" as in "home"), for without it the word חם is ambiguous.
Artscroll gives a delicious example of American Ashkenazic Hebrew (I don't know if the term exists, but the concept surely does). It's explanation of how a קָמַץ (qomats) sounds is '"u" as in "but."'
This is completely correct in that it is precisely how many (by no means all) American Ashkenazim pronounce the קָמַץ. But this is not exactly the way this vowel was pronounced by the various Ashkenazic ethnic groups. Putting aside what has survived as the Chassidic pronunciation (oo as in boot; a normal sound shift), this "u" as in "but" most closely resembles--but is not identical with--the German "o." Other pronunciations of the were קָמַץ essentially variations on this theme, some more pronounced, some less, some closer to "o" as in "home" and some almost like "aw" (as in "shucks!"). Then there is, of course, the Temani pronunciation of the קָמַץ which famously resembles the Ashkenazic, each being me'id on the other. And last but not least, the affectation of some yeshivishe pronunciations which simply can't be produced in any notation I am familiar with.
In short, probably most קָמַץ-pronouncers today do say it like "but," myself included. בָּט this is under the influence of American English phonemes, just as the German Jews sounded theirs under the influence of the German "o."
It is noteworthy, by the way, that in Artscroll's serious scholarly work like the Schottenstein it eschews nonsense like it's constructed Hebrew pronunciation.
Surely a historian of 20th-21st century American Jewry will one day use this valuable footnote to reconstruct the Ashkenazic Hebrew, although he or she will obviously have to be sure about how precisely "but" was pronounced in American English.