Glenn and companion enter the armory and close the door. The door is riddled with bullets from pursuers outside as they duck. When they shoot back we see no bullet holes or damaged weapons in the wall behind them.
At the end, when Morgan is welding, he is using a process called metal inert gas welding (MIG). He is missing the nozzle from his weld gun, this is a crucial component to that process. Without it, the weld would not be covered in an inert gas and would be too weak to be any good.
When Morgan is welding at the end, the MIG gun/torch has no shroud on the end, therefore would not actually weld.
When Rick punches the nose/face of the zombie head made to look like Gregory's, he does so with his right hand, breaking his nose and pushing it to the left. Then he tries to justify it with the alibi that Andy broke his (left) hand breaking Gregory's nose. Andy's left handed punches would have knocked Gregory's nose to the right, not to the left.