I have the following structure in Godot

• Player(rigibody2D)
  • CollisiónShape2D
  • Tanque(Node2D)
    • Sprite
    • Barrel (Position2D)
    • Line2D
    • Punto (Node2D)

and in the bullet instance it is a Rigidbody2D.

Player(rigibody2D)
 - CollisiónShape2D
 - Tanque(Node2D)
   - Sprite
   - Barrel (Position2D)
   - Line2D
   - Punto (Node2D)


extends KinematicBody2D

export var muzzle_velociy = 230
export var gravity = 250
export var Bullet = preload("res://scenes/Bullet.tscn")
onready var posit = $Tanque/Barrel
onready var line = $Tanque/Line2D
var max_point = 250

func shoot():
    var b = Bullet.instance()
    b.global_transform = posit.global_transform
    b.apply_impulse(Vector2(), Vector2(muzzle_velociy, 0).rotated($Tanque.rotation )  )
    get_tree().current_scene.add_child(b)


func _unhandled_input(event):
    if event.is_action_pressed("ui_select"):
        shoot()


func update_trajectory(delta):
    # posit -- position2D
    # line  -- line2D
    line.clear_points()
    var pos = posit.position
    var vel = posit.transform.x * muzzle_velociy
    for i in max_point:
        line.add_point(pos)
        vel.y += gravity * delta
        pos += vel * delta

func _process(delta):
    if Input.is_action_pressed("ui_mouse_left"):
        line.show()
        update_trajectory(delta)
    else:
        line.clear_points()

As you can see in the image, it does not follow the correct angle that projects where the Bullet will fall.