I was given a rifle by my father-in-law, probably over 20 years old. On the left side (shooter's left) of the receiver there is a hole about an inch from the barrel and directly below the scope mount that looks like it would fit a receiver screw, but there is not one in there. Anyone know if this hole has a purpose and whether it should be filled with a screw? Oil access? I've looked at the exploded diagram of a 1500 online, but can't find the hole or screw for that section. Thanks for your help.