I use 16.0 grains of AA#9 under a 240-250 grain lead bullet with great success in my mid-frame Ruger 44 Special Blackhawk. This load approximates the old Keith load using 2400. I came about this load from the Brian Pearce Handloader article. He listed a max of 16.5, which I worked up to, but I had good accuracy at 16 grains so I went back and settled on that charge.

It is a stout load in a smaller framed gun. Personally, I would not shoot it in a 624. At least not frequently.

AA9 is a great powder for the 44 Special, if you want to explore the true potential of the cartridge.