I think that Oswald believed he was sent a 36 inch rifle and subsequently manufactured his rifle carry bag to suit a 36 inch rifle
What a stupid idea!...... Do you actually believe that Lee couldn't have measured the rifle If he planned to manufacture a paper sack??? LOL! 
Not stupid at all, Oswald didn't go to the Paine house since the previous weekend week, and I believe that Oswald only found out about the Presidential Parade in the following week and in the mean time only made his unscheduled sudden appearance to pick up his rifle at the Paine household on the 21st, so if Oswald thought he a bought a 36 inch rifle why should the actual rifle be any different?, of course in hindsight we know the truth but Oswald at the time was clueless.
In the Herald Times on the 19th, Oswald most probably found out about Kennedy saying it would be happy day to oust the Castro Government and that would have fuelled Oswald's fire and when Oswald found out that there was a P. parade on the 22nd, Presidential Assassin Lee Harvey Oswald quickly put his plan into action.


JohnM