When assessing Oswald's rifle skills two factors need to be taking into account: Reguly army qualifies on 300m targets. USMC qualify on 500m targets. Also, qualification standards are tougher in the USMC.
As you can see from the scoring below, scoring marksman in the Marines is pretty close to scoring sharpshooter in the Army, but qualifying expert is about the same in the Army & Marines.
Army:
23/40 (57%) = marksman
30/40 (75%) = sharpshooter
36/40 (90%) = expert
Marines:
190/250 (76%) = marksman
210/250 (84%) = sharpshooter
220/250 (88%) = expert
Oswald was a good shot not only compared to civilians but also compared to regular army rifleman.
Oswald's
first rifle scores and Charles Whitmans USMC rifle scores are pretty much identical. On 1st August 1966, Whitman shot dead 11 people and wounded 31 others,
from 28 floors up. Although Whitman's weapons were far superior to Oswald's and can't be compared, this does show that claiming Oswald to be a 'bad' shot based on his USMC qualification scores is prepositions.
https://en.wikipedia.org/wiki/Charles_Whitman“Every Marine a Rifleman”