You are correct !.............
D|, DF, N| or S|
Indian Government Ammunition Factory, Dum Dum, Calcutta, India. This factory manufactured cartridges for use by the British Army in India as well as the Indian Army. In 1918 this factory was capable of producing at the rate of about 10 million rounds per month. The example at right is of their manufacture. The far right image shows the unusual neck crimp consisting of three parts of the circumference of a circle and three small triangular indents. They produced .303 cartridges in... BCMK2, BCMK2 Special, BCMK6 and BCMK7, BSRP I.P. Mk 1*, BLK, Dummy Drill Mk 1. IP,and IP No 2 Mk 1...................
The 'Z' suffix Refers to graphite glazed nitro-cellulose propellant............