Posting, but late as usual - I hope that I ame xcused for the delay.

PWM's message is as below:

dear mehul

I send you here some more pics
1. from the 1914 collath catalog, the double rifles

2. the cartridge from this catalog

3. the case in the 1904 DWM case catalog, I believe only DWM make it and collath load this cartridge in the dwm case with collath headstamp

4. the tesco bullets in the 1908 RWS bullet catalog
collath give a load of 4 gramm Rottweil Blaettchenpulver No.5 with a 27,5 gramm softpoint
load for the 10,75x68 mauser was 4,2gramm of this powder wiith 22 gramm bullet if i am rigth here.
So I think it was more than nitro for blackpowder
Designation "500x86" is very uncommon for a german cartridge , it have to be 12,7x86R 500 but teschner and collath allways goes their own way.

hope all will happen
lars