Bullet delay stuck and collision

My problem is that I have a despawn timer set up. public float Lifetime = 3; float DespawnTime = 0; DespawnTime += 1.0f * Time.deltaTime;

         if (DespawnTime >= Lifetime){
             DespawnTime = 0;
                 Destroy(gameObject);
         }`
 

there is no error, but when the timer runs out, I can't spawn more bullets. (the bullets are a prefab) My second problem is that I followed the destroy code from a tutorial, and it doesn't work

         void OnCollisionEnter (Collision col){
             if (col.gameObject.name == "Enemy") {
                 Destroy (col.gameObject);
             }
         }
 
 

The code is attached to the bullets. Thanks again!