Old mythology that just won't die.
Mention 30 carbine Blackhawk and the first thing you hear repeated is "loudest gun ever made " or somesuch.
OK, so with surplus ammo it is loud but, like any revolver, but with proper hearing protection entirely doable! Personally, a well stoked 357 is just as sonically egregious to me
That said there is very little surplus ammo left in the pipeline and not a lot of commercial ammo on the shelves.
Therefore, everyone I know that shoots a 30 carb. more than just owning a shock and awe showpiece reloads for it.
With standard pistol powders anything is possible from mild to wild and that includes the accompanying noise level.
Lots of yada, yada but the end result is if you load it like a 32 long that is what it sounds like. And yes, if you fill it up with H110/296 it sounds like a full house 327. Loud, but not worse or magically louder.
Most of the time mine is stoked with 115 gr cast bullets at maybe 1100 to 1200FPS. If you saw me shooting it from 20 feet away you would think 38 spl.
It tis what it tis and what you make it to be.