I have used a lot of Accurate No. 9 in .357 Magnum over the years. Very good Magnum handgun powder, and similar to 2400 in that it offers more loading flexibility than W-296 or H-110. I have watched the gradual decline in loading data for lots of cartridges over the last 35 years and the .357 Magnum is one of the most obvious victims.
Example: Speer No. 9 loading manual shows testing with a 6" barrel Ruger Security Six, with their 158 gr jacketed bullets and 2400 powder, they show a starting load of 13.9 gr with a CCI-550 Magnum primer, with a maximum load of 15.9 gr for 1335 fps. Their No. 12 manual shows a maximum load of just 12.5 gr for 1089 fps out of a 6" Model 19. To paraphrase The Joker in the "Dark Knight", "What happened? Did Speer‘s balls fall off?" I mean, seriously, the maximum load listed is now 10% below the old STARTING load? Of course, the standard answer is "better pressure measuring equipment", different powder formulations, etc. I also believe SAAMI reduced the pressure ratings for the .357 Magnum cartridge due to the K frame Smith &Lessons and later, the J frames being chambered for the .357 Magnum.
So, if you are shooting a robust large frame .357, I would still work up gradually, but I would not worry too much about approaching or exceeding 14.0 gr of No. 9 with a 158 gr jacketed bullet. The Lyman 49th Edition shows a maximum load of 14.9 gr for both 2400 and Accurate No. 9 for that bullet weight.
I am not an engineer, but the old Speer No. Listed the maximum pressure for the .357 Magnum as 46,000 cup, while current SAAMI shows it as 35,000 psi. Can anyone say whether or not SAAMI has indeed "detuned" the .357?