DI is Defense Industries LTD Montreal Canada. I would say if standard loading, then a bullet weight of 174 grs would be correct for it. Some of the ammo made in Canada was non corrosive but I don't know about this round and it being reloadable too.
DI ammo (1941-45) was specifically made with Boxer Non-corrosive Primers, Nitrocellulose Powder of DuPont design, in between
3031 and 4895 ( in Australia we called it "4740" as a surplus powder from 1950s to 1970s.
Ammunition this old will need annealing after first firing, to ward off " age & season cracking". They are extremely good brass ( on a par with HXP from Greece).
Great find!!! Segregate your brass and neck size only for each particular .303 Rifle.
DI also made Boxer Noncorr.
9mmPara and .455 Webley Mk6.