I can't understand how the bag being open at one end somehow lends itself to the conclusion that Oswald did not carry the rifle in it. When the bag was constructed at the TSBD, Oswald would have, by necessity, left one end unsealed in order to put the rifle in it later. Maybe he discovers there is no tape to seal it in the Paine's garage after putting the rifle in it. Or maybe he just decides to fold that end down and carry the bag upright. Most people don't seal their lunch bag shut in fear of the contents spilling out. It suffices to fold the open end down and then not hold it upside down. Gravity takes care of the rest. Maybe he doesn't want to be heard tearing the bag open just before he is getting ready to assassinate the president. Lots of plausible reasons. We can't know for sure, but it doesn't seem like a big deal in terms of whether Oswald carried the rifle in the bag.