Maybe Oswald thought there was coup de uh ta in progress and the Fascists ( whom Oswald hunted) were taking over. Thus , Oswald being a Marxist, must go to fetch the revolver 1st before then searching for another taxi to take him to the Paines house to retrieve his rifle which he must have thought was still there in the garage right?
Come to think of it, why didn’t Oswald just go 1st to the Paines garage get the rifle and also check on the kids and Marina to make sure they were safe?
Oswald knew where his rifle was. Right where he left it on the 6th floor of the TSBD. He probably knew it only had one bullet left in it.