If Oswald had a specific purpose in mind when he ordered the rifle, it was probably General Walker. Killing JFK was a crime of opportunity. I doubt the thought even crossed his mind until he read JFK's motorcade was going to pass right in front of his workplace.
So Oswald using a fake alias name he had used in the USSR and listing that name as an alternate for his own real name P.O. Box and mail ordering a rifle using that fake name and listing that P.O. Box as the address to send the rifle…was because …
A.He was naturally as Stupid as a box of rocks
B.He was aware of how stupid he was acting but he did not care because he was having marriage problems with Marina even before he became fixated on Walker. It was Oswald’s attempt to shock Marina into paying attention to him.
C. He was mentally disturbed from all the way back to his childhood and so it’s not unexpected that he could be this stupid.
D. He was a schizophrenic and Alek Hidell was his other personality.
There, I think that about covers the LN possible reasons for what appears to be incredibly stupid decisions made by Oswald.
Now any CTs still on this forum, please feel free to criticize those above listed reasons and list some alternative possibilities that are more plausible.