It almost looks like your brass had "crimped" primers as in military brass. I have not seen it in 357 but have in 45 ACP.
I have a bag of TZZ (Israel Military brass) with crimped primers.
The Magtech (CBC) looks like a crimp to me.
As to the primer backing out, they will all do that in a revolver if you have no powder and bullet, The cylinder will then get stuck and you say foul words.
When a cartridge goes off (fires) the primer backs out and slams against the breech and re seats, Without the full charge it just backs out and stays out.
I dislike messing with crimps. If it is not a lot of brass, weed it out and use other brass. JMHO I have other things to do than mess with it.