That's the nature of doing proper sound work, I'm afraid.
Often in movies, ever single footstep you hear will have been created in post rather than recorded on set. Often, a seemingly simple sound of a gun firing will actually be a hugely complex sound effect mixing several sources together. Arnie's shotgun in Terminator 2, for example, apparently consists of an actual shotgun, a cannon firing and a lion's roar.
Good sound takes an enormous amount of work - but it's well worth it.