do you mean the best or the cheapest?
the best way for a brass case is a reloading die set. ch4d make such die's http://www.ch4d.com/catalog/dies/caliber-list?page=3

see 12 ga brass shotshell.
tell ch4d what you need and you will get the right thing.
the magtech brass case is to hard so its necessary to aneal it.