>>64442676
>What do they chamber it in? Is there some custom magazine (that thing in the back?) or what?
Yes, that's the mag. Standard capacity was 5 round, plus or minus or a round or so depending on cartridge choice.
They were available built for a bunch of different cartridges. The actions are built to take full length cartridges like 8mm Mauser and .30-06Spr, so any round that length or shorter would fit.
They were offered from the factory in a handful of different full length, and slightly shorter, full power cartridges. Production was at a very limited scale, so they did take custom orders.
If you wanted one chambered for something like .270 win, .243Fudd, .25-06 , 6.5Swede, or 7mm Mauser, they would have built a rifle like that for you.
I believe they also did make some built for even longer cartridges, primarily because cops asked for .300WM rifles.
So if you wanted one in .375H&H or .458Lott, they could have built one too.