Three sentences and three misstatements of fact.
1. Oswald was not a poor marksman. He would have never graduated from Marine boot camp if he had been. The records indicate he scored as a marksman.
2. The rifle in question was an Italian surplus military rifle which was not the best in the world, but far from being inaccurate.
3. He did not use “ open sights”. He had a 4 power scope mounted to that rifle although an average marksman could have easily made those shots of less that 100 yards with open sights.
I'd recommend you visit the 6th Floor Museum in Dallas some day, look out the windows that Oswald looked out of, and see for yourself. At that distance, a quarterback could have hit Kennedy with a rock, let along an ex-marine with a military grade rifle.
I already acknowledge the scope error is post 52. I was using Google as my info source on the rifle.
The source for his level of accuracy came from a couple other threads here on FR.
When I went to boot camp there were three levels for marksmanship. Marksman, Sharpshooter and Expert. Even though he qualified, he got the lowest rating. Speaking for myself, getting Expert was quite easy, as I got it on both the M14 and M16.