This is a very commonly encountered dummy round here in the U.S. I just got a bunch of them yesterday from my local gunshop - they gave them to me. I already had it in my collection, and have had lots of dupes. The “O” on the primer, although identical to the marking on the old RWS Sinoxid non-corrosive primers, has nothing to do with that marking, and simply indicates an inert primer. I am sure the primer is separate from the case. I have the same primer in a dummy AP round from BPD, with standard GMCS bullet, plain, unplated brass case, and green bullet tip. It is inert also, and was probably made for some sort of display, not as a true “drill” cartridge. Maybe tomorrow, I will rip apart of of these and look at the primer a little closer, but I am positive it is not part of the case.