If my identification is correct, this is a Scherpe patroon Nr.4 (short range cartridge) made by Dutch East Indies Pyrotechnical workshop for Colonial army.
As I understand, the headstamp is
FN - case brass supplier, and case was made by Artillerie-Inrichtingen
1 - Powder lot number
21 - Case production year
28 - Cartridge production year
Digits 1 and 28 was headstamped on this case later, after loading the cartridge at workshop
Please, correct me, if I make a mess. I am really not sure in my identification