It's not an attack, it's just good advice. No one should be getting loads off the internet unless the person providing them references the source. What they do personally isn't to be taken and used if it doesn't reference a reliable source. That's just common sense. Do I know what I'm doing? I've been shooting .357mag and .357max in many handguns and rifles for well over forty years. I own several rifles in those calibers and numerous handguns. If anyone needs loading data for those calibers in a rifle I'd suggest getting a copy of the Lyman 50th Edition. They have sections dedicated to .357mag in revolver, TC/Encore single shot, and rifle. That's a reliable source and a good place to look up loads to try. Nothing personal my friend, but safety is primary and nothing beats a referenced, reliable source.
Fair enough. I didn't list loads in my original post because I like for people to look up their own data. I never expected the OP to look up data for midrange loads and thought he would get the 400fps advantage I spoke of. The Sierra manual he used should show the loads with magnum powders.
And like you I have been shooting 357 mag in rifles and handguns for decades and of all the 80+ guns I own my 357 Marlin is my most favorite. If I had to grab one gun and run it would be my choice first and foremost. So no problems here.
To the OP. I have tried many of the magnum powders in the 357 and 44 mag guns but I always come back to Alliant 2400 powder. It is the one I get the most consistent accuracy from with magnum loads. There are newer magnum powders I haven't tried that may be even better but its unlikely I will ever get around to trying them. I have so much powder on hand now I just don't need anymore sitting around.
My favorite midrange 357 load is 6.6grs of Unique with a hardcast 158gr lead bullet. I shoot that load in both revolvers and and rifle. But I don't expect a big jump in velocity from the rifle over the handgun. Its easy on powder and brass. Now I have listed a load on the internet but I feel safe in doing so since its right out of a loading manual and I have been shooting it for well over 25 years without problems.