What is the value of a 1958 Browning 20 Ga Automatic?

Value is too difficult to be accurate without seeing the gun. Condition which includes the amount of original finish and original configuration will determine value. Shotguns with poly-chokes, compensators and added recoil pads (other than Mag 12's) will reduce value. Near mint guns and original box will command an extra premium. Recommend taking it to a gun shop for appraisal.