Here's a little code from my project, which I believe does exactly what you're after:
The code gives the shot initial x/y coordinates.
_x and _y and _rotation are the ship's coordinates and rotation, and yOff and xOff describe the hardpoint offset from the center of the ship.
Hope this helps.
shot._x = _x + yOff * Cos(_rotation) + xOff * Sin(_rotation) shot._y = _y + yOff * Sin(_rotation) - xOff * Cos(_rotation)
The code gives the shot initial x/y coordinates.
_x and _y and _rotation are the ship's coordinates and rotation, and yOff and xOff describe the hardpoint offset from the center of the ship.
Hope this helps.