It wont hit the same hardness (dont take my word for it, get a tester) heat treated after a paint bake over quenching from the mold or oven treating. The closer to slump or a longer "soak"at near slump will create higher BHN numbers.
Dropping them coated from a 400 degree paint bake for 20 mins is probably going to make WW metal be around 15 BHN. Obviously it varies with alloy composition.
Powder coated bullets are an "easy" button, and like you said, cover a lot of sins.
But if I had a reason to do so, I havent found it yet.
You're doing a lot of guessing about heat treating coated bullets, but I have the luxury of speaking from personal experience.
Of course a bullet quenched from 400° doesn't reach the hardness it would from 450°, but if that's the goal, turn the oven up to 450. It doesn't matter how long the bullet is in the oven as long as it gets up to temp, or what kind of oven it is (and we're not using "paint bake ovens", lol); it's the quench that hardens the alloy, not time at temp.
It's always interesting to watch you expound on powder coating though.
And I've also never understood the concern over some leading. Everything is going to lead a little, but I sure as heck am not worried about it. It's like being worried about getting [bleep] on your starfish.
The mistake there is assuming everything is going to lead a little; generally true with lubed bullets, at least a mild lead wash, but not so with coated. A good coating (or paper patch for that matter, they are more similar than different) can prevent any leading, to the point you can fire thousands and thousands of rounds through a barrel without needing to even inspect it for leading or ever pass a brush through it. A complete lack of any leading is a good thing for your own health and those around you, and can contribute to better accuracy that doesn't drop off like when a barrel with lubed bullets starts to lead up.
