There is no conclusive proof that Oswald brought the rifle to work. The "bag" that was claimed to have contained it seems to be of the wrong dimensions. The people who saw him carrying it in state that he carried it in a way which is inconsistent with it holding a dissassembled rifle. Though the gun was said to have been well oiled there was no oil stains on the paper. He was not seen carrying the paper to the Paines house. No one has identified where he could have hidden the gun before use.
Then of course having to re-assemble a rifle makes it even more improbable that it was ready to fire accurately without calibration of the sights.
I do not believe he fired the fatal shot that killed JFK. There are conflicting testimonies wrt the person who shot Tippet and some of the descriptions do not match Oswald or his clothes. Shells were found at the scene though Oswald had a revolver. This raises the question of why they would be deliberately left there by the killer.
Since I do not believe Oswald's role was to kill the president his rifle was unimportant to the killers. Though initially a rifle identified as a Mauser was claimed to be the assassination rifle.
Some believe that Tippet was supposed to kill Oswald and that was why he was out of his district. I am not convinced of that but there was no reason for him to be where he was or to have stopped Oswald in any case. As to the possible spilling of the beans don't forget that we have no idea what was said during the interviews since (contrary to all standard or rational procedure) all notes from the interview were destroyed. That alone should raise red flags galore.