I have recently inherited a .22 rifle. The only markings on the rifle are as follows: O.F. Mossberg & Sons Inc. New Haven Conn., U.S.A. 151M(b) .22 LR Only Pat Pend I can not find any additional markings. It is tube feed (throught the stock), it has a plastic trigger guard and plastic butt plate. It has a 20 inch barrel. The front and rear sights can be manipulated into several different sight picture combinations by loosening the front or rear sight screws and rotating the sights. It is not a bolt action rather it is a semi auto with a pull back knob for the safe or open breach position. Can anybody tell me something about this rifle? It is in near mint condition. I can't include a photo since I don't have a scanner. Since the rifle appears to be new I can only assume that my father purchased it in the '50's or very early '60's. There are no instructions or owners manual so I am at a total loss. Can anybody help?