Does the spiraling barrel of an m-16 cause the bullet to tumble?

Answer 1

This spiraling is called rifling.

This imparts a stabilizing spin to a projectile. The M16 has a very tight spiral, but the bullet shouldn't tumble until it hits a target.

If you picture a bullet, when the narrow tip first hits a target, it will cause the rest of the bullet to tumble, end over end, and often fragment as well.