With safety pins fitted missiles and bombs are reasonably inert. Taking a typical bomb as an example, it takes signals from a device (with various safety systems) to get the cartridges to fire to release the locks and push the weapon from the jet - as long as the safety pins have been left out. From there it is just a crush hazard to anything underneath. For a weapon to go bang the fuse needs to be told what to do, often just after release but before the electrical cable is pulled free and then (typically) it needs a further mechanical line to be pulled free after release. Even then the bomb is not fully armed, needing a time delay or a given airspeed over an arming vane etc before getting to the point where the fuze is live enough to do impact/void sensing/distance ranging before going bang.
A loaded and cocked gun may just need an electrical impulse to fire and may be self-sustaining once firing (depending on type - some guns require AC electrical or hydraulic power to cycle).