You're giving Oswald too much credit on his rifle selection abilities. Military surplus WWII rifles were as common as dirt in the 50s and 60s and tens of thousands of Americans turned them into 'sporters' for hunting. That's precisely what Oswald's rifle was. It was cheap, powerful and effective -- and what he selected ended up being suitable enough. This trend continues into modern times. Witness the tens of thousands of SKS rifles that seem to turn up in just about every shooter's gun safe; I got my unfired 1951-vintage Tula Arsenal Russian SKS-45 for only $75 as a 'Curio and Relic' though it's worth a little more now.
Oswald also had a common budget handgun that he used to shoot Officer JD Tippett, too. The man didn't have a lot of money, being habitually unemployed when not commmitted to menial service labor jobs with a salary paid in 1962 dollars.
What's so suspicious here about his firearm selection?
You're giving Oswald too much credit on his rifle selection abilities. And you gave him too much credit on his rifle shooting abilities.
Still an odd choice for an ex-Marine when more familiar alternatives for sale existed.