This was thrown in with some other stuff I bought as the seller did not know what it was, and I never turn down a free cartridge of any sort. I believe this is some sort of CAD (Cartridge Actuated Device) cartridge, possibly to do with aircraft.
It is made from solid turned aluminium, with a VERY thick head for the size of case, in fact it comes almost halfway up the case. It is electrically fired, with a central brass contact on the head, insulated from the rest of the case by a grey plastic ring secured in with an aluminium disc. It appears that there is no priming charge of any sort, and it is simply fired by means of a spark jumping between the internal electrode and the case wall. There are no markings of any kind other than the remains of red mouth selant. See photos below. I would be really glad if anyone could identify it, thanks in adavance for your help.
Case diameter: 1.680" (27.1mm)
Case length: 1.520" (34.34mm)
Rim Diameter: 1.125" (28.58mm)
Rim Thickness: 0.117" (3.00mm)
Case wall Thickness: 0.042" (1.00mm)
Cartridge from the side (9x19 For Scale):
Case head showing central brass contact, insulation ring and aluminium disc. (9x19 For Scale):
Internal view showing electrode soldered to central raised cylinder. (9x19 For Scale):