Lou, I have FOUR .43 Mausers here..... and less than TWO boxes of brass.
Loading dies are available from Lee Precision, about $30 a set through Factory Sales. They work. They are also made by RCBS but a lot more $$$.
I have barely enough brass for a bit of testing, but I want to use one of my Kar 71s as sort of a "handy rifle", the way I did when I was in high school and loaded ammo was $3.65 a box. Besides, it will be a correct "period" piece to go with my car (a 1934 Ford V8), being that I am a Canadian retiree and not an American bank-robber. Besides, I can't afford a 1921 Thompson! (Can't afford to FEED the thing, if you want the truth!)
I have an idea that .458 Winchester brass could be given a shoulder, held centrally in the chamber by Ed's Famous O-Rings and blown OUT to make a Rimless .43 Mauser which will headspace on the shoulder. Only one part will be needed to make this practical: a new Extractor, which is possible to make. A couple of firings with the SR-4759 and I should have workable brass.
BTW, SR-4759 is ALMOST a "bulk" powder but not quite. Charges are light (38 percent of the original Black load is safe in most old rifles and will produce the same velocities AND pressures as Black at that loading level) but the powder itself is reasonably bulky, although the new stuff does not seem as bulky as the tin I bought 50 years ago. But here is a thing about SR-4759: you don't need any pressure or a wad on it at all; the bullet is enough for it to build the right pressure, even though the case may seem only half-full. It is VERY quick.
When I was still in school, I took apart a live DOMINION round of .43 Mauser. It was loaded with some strange PINK powder which looked for all the world like the photograph of LESMOK in Hatcher's Notebook! And there really was not a lot of it, either. And NO wad.
Correct bullet diameter is .446", although the BORE diameter is .433". I had a .457-405HB mould (Lee) which I loaned out to a friend. He promptly fell in love with it for his Martini, so I have to get another. But he did bring me a nice tub of bullets cast from it, lubed and then run through a .446" sizing die that he made in his shop, so it CAN be done without buying one of those $100 moulds. The Lee mould which I started with lists at about $30 from Factory Sales.
Hope this helps.
Let us all know what progress is being made!
Be good to see these old-timers back where they belong: on the range or out in the field.