Well I now own the Mahillon that was the subject of this thread. It is a full blown nitro with a .510 bore and a case that is 70mm (2 3/4") long with a sharp neck at the 2.3" point (like the 500 Jeff), made from 577 nitro brass (.750 rim, .660 base). The rifle was made in 1923 by an unknown German maker, and retailed by Mahillon in Brussels. It has a very unusual front sight with a fold-back square protector, and both a fine and a moon bead. The barrels are chopper lump with German proofs. Recently it has been completely restored and restocked by an unknown person. I intend to work up some loads with the correct 34 gram bullet (525 grain) and see how close the leaves are (50/100, 150, 300). I suppose starting with about 90 grains of 3031. Next time I get to Africa I will clobber something with it.