How is the gun marked on the barrel? Moss made several left hand rifles but that was before the war, the 44us is post war. In 1937 Moss. introduced the 'Master Action' and receiver, its basic design and dimensions remanded the same into the post war period on all bolt models of .22's. I would suspect that someone married a left hand receiver to 44US parts and stock.
Go to RimfireCentral.com, Moss forum, where the Moss. collectors hang out. I believe there were few models made with left action but all had a L in the model number, at least in the literature. I do not think you have a factory original rifle.
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