What is value of browning sweet sixteen with gold trigger purchased in 1964 used once and kicked too hard. Has modified choke 28 inch?

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. Auto 5's with recoil pads (other than Mag 12's) poly-chokes and compensators will reduce value. Sounds like your gun is near new condition, but with over 40 years of storage, it can put some wear on a gun. Recommend taking it to a gun shop for appraisal. As far as your comment about the gun kicking, Browning A5's are some of the easier recoiling guns ever made. This statement has been made by many owners before. Usually it is a simple case of the friction rings being set for heavy or light loads. This is a 2 3/4 chambered gun. If you shoot a heavy load like High Brass 4's, 5's or 6 shot, and the gun is set for light loads, the gun recoils hard and you will feel a real kick from it. The brass friction rings need to be set for the heavy loads to shoot those shells. It is a world of difference in felt recoil. Back in the 60's, heavier 16ga shells were available more so than today. Now lets say you are shooting lighter loads for dove and quail or trap shooting. If the gun friction rings were set for heavy loads, chances are the gun won't eject the fired shell. To change the rings is simple. Remove the forearm and the barrel. The rings are on the magazine tube. For a diagram on how the rings should be set, you can visit the Browning Companies web site for a diagram. Print the diagram and cut it out so it will fit inside the forearm. Use a little glue to keep it against the inside of the forearm. Now you can change the rings easily with the diagram right there.