
Originally Posted by
Charles E
How? When you neck down, less of the old neck is in the new neck, unlike necking up. You're not going to lose uniformity of wall thickness in necking down.
It is necking up where part of the old neck/shoulder junction is moved into the new neck (if you keep neck length the same).
Necking up is likely to cause more non-uniformity than necking down, but I'd think that some would likely occur with either. The brass in a necked down cases neck gets thicker, but I've never measured cases that I've necked down because they're going to need turning anyway so sure wouldn't swear to any non-uniformity before turning.