although a existens of 10.75 x65R Collath was doubtful for me since a long time I investigated this case without prejudice.
if it would have shown that the cartridge exists, why not?
We have too little information about many old german big bore cartridges . the conduct of the seller of this weapon have show me the truth. if you have ammunition books in which the 10.75 mm Collath is listed you can make a tick behind the cartridge - extinct