Oswald got lucky... probably

"Perhaps Oswald didn't know he was going to use the irons until after he fired the first shot while looking through the scope."Dear Chappy Dumbster.... Nobody with an iota of knowledge about firing a rifle would propose a theory as stupid as Billy Boob Brown proposes.
First off the idea is utterly insane because after just one shot there is no way a gunman could know in three seconds that the scope was out of alignment.... It takes a second man (a spotter) who is watching to see where the bullet strikes to enable a rifleman to know how he must adjust his aim before firing his second shot......
After a single shot a sniper would have no idea if the scope was misaligned or if a bit of rust or dirt in the barrel, or a malfunctioning cartridge, caused the bullet to miss the target .... After a single shot there would be no reason to switch from the scope to the iron sights..... ( The brief time period of six seconds would have prohibited switch from scope to iron)