Compounding the difficulty of getting a second shot off is the transition from inaction.
If Oswald didn’t have a spotter, then he would have been waiting for some time for JFK to come down the road, while the tension mounted. Then switch from scanning to scope. Pull the trigger, make the decision he needs another shot, and start cycling the bolt.
On the other hand, if there was another shooter, how did they know when to shoot? Especially if Oswald didn’t know of their existence.
Could a spotter keep an eye on Oswald and JFK?
Years ago there was this theory of triangulated fire, being three shooters that was well coordinated. Personally I never believed there were three active shooters.
But a good hit team could have a well planned attack that would be coordinated. Planning, training and rehearsals of professional shooters with quality weapons could have pulled it off.
There’s not enough information to know exactly how two shooters could have had their shots so well timed. So a person would have to guess. The route of the President was obviously well known. The shooters could have been set up to fire only when the vehicle was in a certain area. When in that certain area the weapons would be zeroed in on Kennedy. The cue for the second sniper to fire could simply be hearing the shot from the lead sniper. This is all guess work, but plausible.
The only thing I’m confident of is if Oswald shot at all, he could not have gotten off a second accurate shot in that 2.3 seconds. If he did get off that first shot, then that would have been the cue for the real sniper to get off his shot.
The shooting distance was 88 yards. At that range does one need a spotter? At that range, with a quality rifle, a scope really isn’t needed for a professional shooter. I have my own rifle range. At 75 and 100 yards I can hit a head size target with my M16 that has open sights. A quality hunting rifle of the era could do the same.