I agree with Sir Ron that the best powder for both the 300 and 350 TSX's is H4198, so also for the 300 Shock Hammer. IMR 4198 is NOT an equivalent powder.
In my 24" Ruger 1H, I was able to safely attain up to 2980 fps from the 300 TSX, and into very tight and consistent 3-shot groups at 100 yds. And, from the same H4198, 2780 fps from the 350 TSX shot into sub-MOA. I'm not authorising psi, but those appeared completely safe in my rifle, and I wouldn't shun from using them in the field. In fact, the 300 TSX became one of my all-time favorites from that rifle. Alas, I shot them all up in load development and practice.
However, agreed that the 400 Shock Hammer is preferred as an "all-rounder".
