The banjo never needs tuning, nor does the piano in the middle of the jungle or desert which remains at concert pitch.
The hero, whether he has any bomb disposal experience or not, will always defuse the bomb with a second to spare. The baddie will have provided it with a LED display to make it easier for them but hasn't fitted it with any anti-handling device!
When the hero gets a .38 slug in the shoulder he doesn't have a 12" exit wound, just has his arm in a sling in the next scene with a 2" bloodstain on it. By the following scene he's using both arms to box like Joe Louis.
RtS