I just can't buy into that line of thought.
The only "magic bullet" that exists is the one that you created that was supposed to come from the Grassy Knoll.
If anyone had shot from the Grassy Knoll, Zapruder would have heard it come from there. He did not.
Try to pay attention. Kennedy was hit only twice.
He took one shot at Walker, through a window. I don't know how well he could see his target or what the distance was. On a day prior to the assassination when Nixon visited Dallas he left the house with his revolver and told Marina that he was going to see Nixon and would use it if he could. In this state of mind, willing to do these things, he sees in the paper one day that the President is going to be driving right by the place he happens to work. It didn't take much thought for him to decide what to do.
That rifle may have been old, but it was an Italian military rifle. They didn't use it because it couldn't shoot straight. It was known for its penetrating ability. There is no "magic bullet". That is yet another myth created by the early conspiracy mongers. The trajectory from the window to Kennedy to Connally is a straight line trajectory. No physical laws were broken.