Ben: like me, you must have gotten your hands on the first Vihta Vouri load data. In the first edition they took their .357 Magnum load data up to 44,963 PSI/CIP. The European CIP measurement system is very close to our CUP pressure measurement system. These loads were close to the older CUP pressure max of 46,000 for the .357 Magnum and near 50,000 PSI in the piezoelectric PSI system currently used by most ammo/component makers in the US, although a few have reverted back to CUP testing where magnum loads have gotten a little closer to the original CUP spec. I'm sure V-V wanted to impress us (the US) early on with their powders' performance, but they went to that level with all of their pistol powders, including their very fastest, N-310, which ranks a few numbers faster than even Bullseye. In such an extreme pressure range, yeah, I could easily understand where even a .1 grain increase over the previous charge could spike pressure, but only N-110 should have been used in the upper pressure range. I could hardly imagine that someone would choose N-310 (3N37 for that matter) to build such a load, but there was an article in Shooting Times when V-V powders first hit the street over here, and the author/reloader did take 3N37 with a .357 140 gr. JHP up to the extreme max level. Performance was impressive as was accuracy, but not a good choice for a extremely high pressure magnum load. Consequently, the max load in the second edition was the same charge as the start charge in the first edition. Pressure was 36,300 PSI/CIP.
What I took into consideration when I first started loading the .357 Short Magnum was the fact that .357 Magnum revolvers that will chamber the round can fire .38 Super +P ammunition with its much shorter case and pressure rating of 36,500 PSI. I never intended to take the .357 SM above 35,000 PSI. In truth, with the powders I've used, that did also include Blue Dot early on, I doubt that I've gone above 30,000 PSI. I discarded Blue Dot because of flash/muzzle blast and went to V-V 3N37 which is a bit faster and similar to IMR 800-X in burn rate. Blue Dot, or 800-X could be used for this type of load if muzzle blast is not an issue, like say for a field load. I haven't used 800-X, so I can't say for sure what flash would look like. The intended purpose was to find a powder that would achieve the desired velocity with a quicker pressure peak than say H-110, W-296, 2400 ETC. Some believe that pressure peak occurs in revolvers before the bullet has left the cylinder. I am not of that school and there is a very good technical article on the distance of barrel length required for pressure peak to occur, in the Lyman manual (Mine's the 46th) and was conducted for the US Army by H.P. White laboratories. It is a minute difference with time in microseconds, but it concludes that pressure peak occurs in the bore. With differences in burn rate, pressure peak occurs at slightly different distances in the bore. That's why I went with faster than magnum powders with this load intended for short barreled magnums. I used a 3" S&W model 65 for testing. Magnum powders have a higher velocity loss as you shorten the barrel, so finding a powder that has an optimum pressure peak for the length of the barrel is how I approached it. My shooting partner had a 4" Taurus Tracker 7-shooter that would not extract full length .357 Magnum cases without difficulty. The .357 SM also solved that dilemma. I recommend it to experienced reloaders that do shoot warm loads in Smiths with the shorter ejector rod, because it will extract, and while giving them all of the velocity they'll want from a small revolver.
At Accurate's website, they show load data, or did, above 43,000 CUP. The difference in velocity of the max charges of AA#7 and AA#9 is very slight in relative terms (especially with 150/158 gr. bullets) except for guys that really do go to the max., and I have loaded for the .357 Magnum Redhawk as well, so we know what that's about. Not the kinds of loads one is likely to use with a 4" K-Frame Smith, I hope. As you shoot the loads in revolvers with shorter barrel lengths, the slightly faster pressure peak of AA#7 will allow it to hold velocity better in the shorter barrel vs. AA#9. I mention #9 because I use it and love it in full length .357 Magnum cases. It is similar to 2400. Flash is much lower and complete ignition more likely. This is not a knock against Unique or 2400 for the guys that use them, but rather a recommendation for something in-between to optimize performance to the shorter barrel length of revolvers 4" and shorter.
Yikes!! I'm not pulling the trigger though.
