Try air-cooled and see what happens. Heat-treated 50/50 isn't needed for much of any kind of shooting until you get way up there in velocity, 2,000 to 2,500 fps and over 40K peak PSI.
2400 is also something to try. Fiver was talking about this a little while ago in another thread regarding filler, powder position sensitivity, and load workups. 2400 is very position sensitive in large cases and can be very erratic until a certain pressure point in the system is reached. With a light bullet cast of an alloy which engraves easily and presumably using light neck tension and no crimp, 2400 may need some help with a little Dacron to burn consistently until you get into "needing gas check" speeds/pressures. Dacron, if used "properly", is more than a powder positioning device; it can "fool" the powder into thinking it is in a smaller case than it actually is, can act as a pillow against the bullet base to stop gas-cutting, gas leaks, and help protect the bullet base for a few critical milliseconds until the bullet is pushed safely into the throat. I often use Dacron with my "plinker" loads in .30-30 and .30-'06 even with Unique powder because I see so many benefits (reduced throat leading, better accuracy, cleaner chamber necks), especially with very lightweight, plain-based bullets. Dacron is a pain to use but sometimes it really helps if you need to employ a relatively slow-burning powder in a situation where it normally wouldn't be making enough pressure to burn completely or correctly. How hard you seat the bullet against the throat or let it jump also affects the burn curve. Seating the bullet to touch something is probably where you want to be with 2400, but not so much with Unique.....most of the time with systems like the one you have here. Only experimenting with your particular collection of stuff will tell you for sure.
Notice that Ben doesn't use Dacron much if at all with his target loads. Also note that he uses medium-burn-rate pistol/shotgun powders and usually uses an alloy like air-cooled clip-on WW plus 2% tin. This combination is well-balanced for a lot different cartridges and rifles within the velocity and pressure window he typically uses. This balance is one of the main reasons why he is able to get very good groups. If he were to switch to something like 3031 he would be fighting ignition problems and have to bump the velocity, pressure, alloy strength, add some neck tension, maybe add some crimp, maybe use a filler or even a buffer, etc. If he were to use a tougher alloy, he might have to again bump the pressure and tinker with the pressure curve (different powder burn rates) to get the same launch dynamic and accuracy back again.