Hey- you have just not run into a pack of Mossbergaholics! Vicious critters, they are!
Your rifle was made 1944-1946. It is the civilian version of the military trainer- and the first of the 44US series that had an adjustable trigger. Here is some good info on Mossbergs for you: Mossberg 22 LR Models and Specifications
Scroll down to the 44US, shows the variants, and note the blue letters that link you to more info.
Enjoy- those are some tack drivers. If you need parts, check out havlinsales.com. Vic Havlin and his wife Cheryl are really nice people, among other things, run the Mossberg Collector's Assoc.