Does your gun say US Property and have a serial number? If you go to rimfire central forum, you will find out a lot under the mossberg forum. Great bunch of guys on that forum.
From the Homeepix site:
Model 44US bolt action repeater.
22 lr, 7-shot detachable box magazine. 26" heavy barrel. Weight 8.5 lbs. Target stock, swivels. No. S106 ramp front sight, No. S100 receiver sight. Made 1943-1945.
Model 44US(a) adjustable trigger pull added, made 1944-1946. Exploded View , General Instructions , Disassembly/Assembly of Mossberg US44 Commercial Rifle
Model 44US(b) change mad in extractors, made 1946-1947. Exploded View , Disassembly/Assembly of Mossberg US44 Commercial Rifle
Model 44US(c) S130 sight replaced S100, made 1947-1948. Exploded View , Disassembly/Assembly of Mossberg US44 Commercial Rifle
Model 44US(d) new front swivel, 3 position, made 1948-1949.