I case you can't find the thread, here's the
TightNeck experiment, from back in 2012. While my effort was not as extreme as the ones pictured in this thread, the concept is sound
except for two issues. Brass is not hardened by heating and quenching like steel is. It is hardened by working it. IE stretching and shrinking the wall thickness. It increases the brittleness of the brass. For reloaders, that usually happens after multiple reloadings over time with normal resizing, eventually requiring the reloader to anneal the brass. The other issue is when you squeeze the diameter down, the cases gets longer and you would have to trim them back after the extreme resizing to make the SAAMI spec length. Once fired and they expand to normal diameter, they will be shorter than SAAMI spec, even after resizing them to normal 450b diameter. Some members here buy commercial ammunition and sell their brass to reloaders to offset the cost. As a reloader, I would be cautious about buying those TightNeck cases from someone sight unseen. You may find that once you resize them to normal 450b SAAMI dimensions, that they are too short to make spec.
I totally get this vendor's approach but I don't understand why they extreme sized them so far down the case. As my original experiment in the link above mentions, you only need to squeeze the case down as far as the seating depth of the bullet, to realize the benefit. My hat's off to the vendor for being able to mass produce these though. Getting a non-boat tail bullet to start down those narrow for caliber necks is really tricky, even with the superior Hornady seating die, with its bullet aligner sleeve.
Hoot