I believe he used the iron sights. That was his only choice as regardless of shims at all, Oswald would have known that disassembling a rifle, placing it in a paper bag, and then assembling it inside the TSBD would mean the scope could not be trusted as it had not been zeroed in in its assembled state which is the only way to zero in a rifle.
But the scope as the FBI found it needed to have shims. Did Oswald have shims prior to the assassination or is it possible that Ruth Paine damaged the rifle scope in her car and therefore while the rifle initially might not have needed shims, after Ruth Paines car journey the rifle would now require shims.
I believe he used the iron sights. That was his only choice as regardless of shims at all, Oswald would have known that disassembling a rifle, placing it in a paper bag, and then assembling it inside the TSBD would mean the scope could not be trusted as it had not been zeroed in in its assembled state which is the only way to zero in a rifle.HOW, ??... would Lee have known that disassembling the rifle, placing it in a paper bag, transporting it, and then putting it back together again would require a re-zeroing of the scope? There's no record of Lee ever using a rifle with a telescopic sight...So HOW would he have known??
But let's say he was aware of that problem.... And if he was, then he would have known that he would have to fire the rifle using the scope and examine the target, to determine what he would need to do to zero the scope. If Lee had been the assassin using that Carcano.... and he knew the scope was worthless, then he could easily have removed the scope....
I'd suggest that you give up the idea that Lee Oswald was the assassin who was brilliant on one hand and an idiot on the other.