tunofun:
The 12-bore brass cases are a bit hard to find in Oz, Saunders used to stock the berdan-primed CBC cases at Century Arms, someone here may know of a current supplier. In the States its obviously much easier.

Note that historically, 12-bore guns designed to fire brass-cased cartridges have a slightly larger bore diameter than those designed for paper or plastic cases.

Many buff have been laid low in the NT by 12-bore Brenneke slugs, but the Foster-style slugs as loaded by Winchester are hollow-lead inverted cups and are woefully inadequate. Great on pigs though.

If you can use a rifled barrel or rifled-choke barrel, Fosbery-style slugs up to 750 grains are a far better option, and are very effective on buffalo. The chapter on loading for the Paradox in Graeme Wright's book is the best source of info to date.

Another slant on this has been commercialised by James Gates in the US: check out the Terminator and Xterminator slugs in the product range on his Dixie Slugs website: http://www.dixieslugs.com

Hope this helps.