Lag on Collision from Projectile

Basically I can run around/look at all my game objects with very high FPS, but as soon as a bullet hits an object next to a bunch of other objects, it drops to <5 FPS. Also note that I can hit single objects away from other objects without a FPS drop. I turned off oncollisionenter with the objects so it's not doing anything once the bullets hit the object, and the bullets also delete themself upon impact of a rigidbody, so really, all that should happen when I shoot an object with nothing happening in it's oncollisionenter, the bullet should just delete itself, so why the FPS drop? Am I missing something?

My bullets code:

function Start()
{
    yield WaitForSeconds(0.3);
    Destroy( gameObject );
}
function OnCollisionEnter( collision : Collision )
{
    Destroy( gameObject );
}

The gun's Fire function

function Fire()
{
        if (PauseMenu.isPaused == true) {return;}
        var instantiatedProjectile : Rigidbody = Instantiate(
        projectile, transform.position, transform.rotation );
        instantiatedProjectile.velocity =
        transform.TransformDirection( Vector3( 0, 0, speed ) );
        Physics.IgnoreCollision( instantiatedProjectile. collider,
        transform.root.collider );
}