As said, a lot depends on why it is loose. If the threads are shot or stripped or if it simply has been rotated to where the nipple is too far forward, etc.
If the barrel threads or drum threads are shot, the drum must be replaced and if the barrel threads are the problem, it will need to be replaced with one with a larger threaded portion.
If it is rotated too far forward, a thin washer could be used.
If the drum is not well supported by the lock, the drum could be in danger of shearing due to the hammer impact. This would need to be solved.