I should have said this in the first place: Citing "Youtube" as a source is almost meaningless. It's only one step above citing "the internet" as a source, and two steps above citing "some piece of paper with writing on it." In a sense, when us hoi polloi take up discussing subjects such as the metallurgy of an alloy like brass, we are all completely over our heads. It doesn't help, though, to be accepting some guy whose claim to fame is owning or borrowing digital video equipment, then running his mouth about something he may or may not know anything at all about... as an "authority" on the subject... any subject!

So far as I'm concerned, though I make no pretense of being an authority either, whoever the guy in question is, may have handed you half a ball of wax. I think that if you look further into the matter... some place more authoritative than "some guy on Youtube"... there are two aspects to annealing cartridge brass: (1) evenly heating the appropriate part to the correct temperature, then (2) quenching. Heating alone will soften the brass. Quenching restores a certain amount of hardness, but without the brittleness that existed before heating. As a part of protecting the case head from becoming soft, it sits in water so that it never gets very hot... then the moment the part of the case that is being annealed reaches the target temperature, it is tipped over into the water and quenched.

At least, "That's my story, an' I'm stickin' to it."

It may well be that your Youtube guy includes quenching and you just didn't mention it. But... your synopsis sure doesn't sound like quenching is even possible using his "method". I f you can't be bothered with providing a specific URL to the specific video you are referring to, though, I can't be bothered with looking at random videos till I think MAYBE I've found the one you are talking about...

Sure, I look at Youtube videos too... and pseudonymous internet posts. But when it comes to holding something that goes "BANG" in front of my face, I sure do like to depend on something somewhat more authoritative. It appears to me that you are about to turn your brass to mush.