I am not sure about preventing fingerprints, but Oswald was wearing some of tools that can be used to remove them. Or do you think Oswald was too stupid to know that he might leave fingerprints on the rifle and that these could be used to identify him?
Do you realize how difficult it is to remove all your prints from a MC after you have disassembled/reassembled and fired, then ditched it? Impossible! And Shirley, Oswald realized that a printless rifle would still lead back to him, regardless of whether they snuck a post-mortem palm print on the stock.
Which leads us to why would military marksman Oswald, who knew a thing or 2 about rifles, keep a useless scope on the MC when he knew he would have to use the iron sights? Especially, if he smuggled it disassembled into the TSBD in a too short paper bag? If you counter with, Oswald didn't know the scope was useless because he hadn't shot the rifle before, then you have to explain how phenomenal it was that a rusty marksman pulled off 2 for 3 hits in 10 secs on a moving target with a wonky scope?
Oswald must have looked thru the scope, lined up JFK's head and hit Tague with a ricochet off the pavement. He must have noticed the small dust cloud from the 1st shot and re-calibrated his aim thru the scope for the MB shot, and what a shot it was. 7 wounds and very close to a head shot, all after bolting in the next round and re-aiming thru the wonky scope.
It took 3 shims to realign the scope on the MC before the FBI could even hit the target. The scope was useless and the big question is whether Oswald knew this and used the iron sights instead. And if Oswald knew the scope was useless, then why did he keep it on the gun when he smuggled its parts into the TSBD?
Answer: The scope was left on the gun (which was never disassembled/reassembled BTW) because the MC that was planted on the 6th floor needed to match the backyard photos of Oswald holding it. Sheep dipping 101. Otherwise, there is no way in hell that Oswald could have not left a single print on the stock, barrel, bolt, trigger, clip and ammo. Impossible.