On his first attempt, Oswald barely qualified for “sharpshooter” — the second of three levels (below it is marksman, above it is expert). The qualifying score was 210, and he shot a 212. The second time, he just missed, and qualified at the top end of the marksman class (195).
He was below average for a Marine. Thats still well beyond the average civilian.
A couple of observations: 1) Maybe, just maybe Oswald practiced just a bit after he got out of the Marines. People act like he was this crappy shot and never picked up a rifle again until the day of the assassination 2)Connally was sitting much closer to the center of the front seat which makes the magic bullet theory less plausible. The shot makes almost a straight line through Kennedy into Connally when this is taken into account. 3) Kennedy's head moves backwards, but even if the "frontal shot" didn't happen, the acceleration of the car would have made him slump back anyway. 4) They have done studies that the head WOULD have moved backwards from a rear shot because of the momentum of the brain material being blasted forward 5) I've been to the grassy knoll and even though it was a train yard in 1963, the shooter would have been a sitting duck, completely exposed and very easily caught when he tried to make a getaway. 6) Dealy Plaza is a very cavernous space, surrounded by buildings. There would have been so many echoes that it would seem as if shots were coming from every which way. 7) Oswald had a motive. He was known as a Communist and JFK was very anti-communist (I know, imagine a pro-American democrat). What a grand way to strike a blow for his comrades. I used to believe in this conspiracy nonsense, but it's just an exercise in mental masturbation.