You seem to have an earlier one of the 1640 actioned rifles with the steel triggerguard and floor plate, rather than the later alloy ones. A good thing in my opinion. Seems to be a 1956 model by serial number. With a 20.5" barrel and Monte Carlo cheek piece I agree with a 4000 model most likely. But I am not entirely sure if they called them 4000's in that 1956? Maybe someone else knows on that. You said it has an outline of the front sight. Is there a dovetail cut for a rear sight by chance?
