The comments about current 2400 being faster are very much on target, no pun intended. I had to reduce Elmer's old load to 20.0 gr. in my S&W 629, and like others, it ain't what it used to be.
Taker a few of those bullets (not cartridges, just the bullets themselves) and drop them into the chambers as if you were loading ammo. They should be a very snug fit as they slide though the throats or be tight enough that you need a pencil or dowel to get them to go through. If they just fall through, then the bullets are too small. next, drive a slug through the barrel and measure the groove diameter. Could be difficult if you have an S&W as they have five groove barrels, which are, to be perfectly blunt, a bitch to measure. Best you'll come up with is an educated guess. You could try the slug in the chambers and it should slip through fairly easily if the bore is correct.
FWIW, when Alliant took over making hercules' powders, they changed one of the ingredient in the making of the nitrocellulose, with wood fibers (sawdust, if I understand it correctly) replacing the more expensive cotton linters. Now, if it is now being made more cheaply, why did they raise the price?
I just had to say that.
I still use #2400 in my .357 mag. loads and for some mid range cast bullet rifle loads , but have gone to W-296 for my full power .44 mag. loads. FWIW, I shoot only my home cast bullets in my 44s.