Is it 2d/3d ???
If it is 2d then create a line factoring in the angle of the gun and other variables don't draw it on the screen, just keep track of the end point.
In the current frame if the user click on the FIRE button, before rendering the next frame load the texture of a bullet hole in the target area.
If its 3d, schedule another talk with dad.
This is me, just "shootin in the dark" :wink.
Hope i have helped.
Edit: You are using an engine, i gave you the logic i am sorry i have no experience in DARKDGK engine.
Edit2:I assumed that the bullet travels in a straight line, from the barrel to the destination and then you stop tracking the bullet.