This cartridge had been misidentified and sitting in my collection for eons. I have consulted COTW, this forum, and websites, without success. The bullet measures 0.380 inches in diameter, dimensionally the cartridge is 9.7x57Rmm. There are no headstamp markings.
I am too embarrassed to say how I had cataloged it, other than to admit, once upon a time, I occasionally accepted vendors’ descriptions at point of sale without verifying. Pending identification, the good news is that I don’t have a similar cartridge elsewhere in my collection!
Any help would be appreciated.