I suspect that the problem you will find is that the appropriate charge of Red Dot in the gargantuan case is going to give you erratic results with each shot. Tip muzzle down before fire and get one result... tip backwards before fire and get a different result. This situation is specifically why they came up with Trail Boss.
In this situation, I don't like Trail Boss -- I prefer Titegroup, because Titegroup doesn't seem to care.
I'll admit that I have never tried bunnyfart loads with any powder in .460/.500 Mag, I would imagine a LARGE shift in elevation might be likely? I'm almost always in the camp of handloading enthusiasts that NEVER care "why", I believe any/every safe handloading adventure has merit and I ignore folks who bash odd ideas. But for my own needs, the big revolvers are actually too damn gangly to enjoy using with light stuff. So my .460 aims for 2,000 fps at the muzzle.
I like to swap brass... and I'm looking for .32 H&R Mag, .327 Fed Mag, .380 Auto and 10mm. If you have some and would like to swap for something else, send me a note!