1) No. It’s possible one or more of the cartridges that your bullet strikes will ignite, but it won’t be a “chain reaction” sort of thing. Without being constrained in a chamber and barrel, a cartridge going off is actually considerably less powerful than when properly fired.
2) Not specifically, no. Commercial ammo is typically packed in carboard boxes, contining a seperator of some kind to hold individual catrtridges in an orderly fashion. No armor, no damage resistance apart from genral shipping packing.
Military ammo is somewhat better protected, but typically just against handling and transport damage, moisture and dirt/grit, and preloaded into stripper clips, belts, or magazines.
3) No. Chances are you won’t even get one cartridge to “go off”, and you’ll have ruined the magazine and it’s contents. If a cartridge did manage to “go off”, it would be slightly more powerful than a firecracker, but the bullet would probably not exit the body of the magazine.
4) Depends on which movie. Typcially, a centrfire cartridge tossed into a fire will simply reach an ignition temperature, go “pop” and throw the bullet perhaps two or three feet.
Again, if the cartridge is not constrained by a chamber and barrel, and the internal pressure is not allowed to rise as it wants (the powder burns faster the greater the pressure- little or no pressure, as if burning it in an open pile, and it burns relatively slowly, as in seconds, not milli or microseconds.) The pressure simply reaches the point the bullet is pushed out, the pressure drops, and the rest of the powder just burns away.
It’s not smart to put ammo in a fire, but it’s not “Darwin Award” dangerous either.