Gday Evan , welcome to the forum !
i'm no IJ expert but off the top of my head
Small frame 7 shot 22 rimfire caliber with prefix =D (1909-1917) and A (1918-1941/1942)
so by my reckoning its safe to fire using standard velocity .22 LR and being post 1918
NOT a black powder gun
as for date of manufacture i cant help but i reckon by morning our time you'll know that too from the real experts here
(i'll guess pre 1920 )
Nice to see more Aussies jumping onboard
cheers and again Welcome !!
added a pic , is this your critter ??