Seems more reliable than the original method but not perfect. Added number based weapon switching

scripts/rocket.gd

@@ -14,7 +14,7 @@ var player_position
 
 # Called when the node enters the scene tree for the first time.
 func _ready():
-	linear_velocity += transform.basis * Vector3(0, 0, -bullet_speed) + player_velocity
+	linear_velocity += transform.basis * Vector3(0, 0, -bullet_speed) 
 	blast_radius = radius_shape.shape.radius
 
 # Called every frame. 'delta' is the elapsed time since the previous frame.