Just wow lol. No need to fire a weapon. All you do is run in and pistol whip them. The case will drop. Run out and get in your car or friend's car or helicopter.
So guys some people told me when they try to pistol whip they will get shot... The secret is that if they drop their gun and the gun hits the ground and discharges a round they will start to shoot you. To counter this, try pistol whipping at most 5 enemies. They are much less likely to fire.
Again, I do not claim this is how you should do it just how I like to do it and it certainly has some advantages - quick, easy, little damage taken, no ammo cost.
Good luck, happy hunting.