I tried five Lyman 457193s yesterday over 11 grains of Unique just to see what was possible to stabilize subsonically. These weigh 413 grains in my current alloy. Actually they didn't shoot that bad. I got a 3" group at 100 yards, (1/2" vertical dispersion, 3" horizontal dispersion). Considering they were the last five shots out of 60, a lot of that horizontal dispersion was probably me as I wasn't really working at it. I just wanted to see if they'd make round holes, and they did. I lubed them by hand, as I don't have a .458 lube sizer die, and then sized them to .452. They hold a lot of lube, and they were smoky, but they shot pretty well. Next time I'll try some out of a clean barrel when I'm really paying attention. AV was 1030 fps, ES was 29.24 and he SD was only 11.18. High Velocity was 1040 fps, so this could make a reliable subsonic load. Might be it could even be bumped up a little. I did need to hand cycle the action, which is not a bad thing if your intention is to be quiet.
BD