NOTE: SEE CORRECTION AT END OF THIS THREAD.
I have a brass case I picked up at a local gun show a couple of weeks ago. It measures 40 X 272 mm. Head diameter is 63 mm. Rim thickness is 6 mm. There is an annular groove 5mm wide by 2mm deep. The impressed headstamp is “L inside a triangle” (I assume this is an inspectors mark), “7-42” (original date of the case), “LOT N00399”, “40 MM MK-1”. Black stenciling on head “17-HA-53”. On the side of the case is black stenciling “UG-62-HA-53”. I know the black stenciling means that the case was re-inspected or re-loaded. Who is the original maker and who is “HA” and what does “UG” mean? I can not find this case length listed in any of my references. I do not think it has been cut down. the case is tapered like a 40 x 311 and bottlenecked. What gun was it for?