Fuhrman is right, it isn't the bottlenecked 11.15 X 60R case head, aka Mauser "A" base. At least not according to my 11.15 X 60R. I measured one of mine curious to see if it might work as a parent case, not even close.

I've have some interesting excursions with old, unidentifiable German cartridges. Each one more interesting and fun than the last.

Fuhrman will have to answer definitively but I do believe Horneber is still in business.

Furhman, thank you for posting that sheet. I have a T&S drilling stamped "XX X 74 1/2". What you posted is the first time I've seen any of the Nimrod cartridges specifically shown and mentioned. I also have a 10.5 X 47R in a combination gun. Pretty cool to see it on the sheet also!!!