There are several ways you could align the camera view to the weapon sights.
Animation:
- Requires some effort to make sure the sight is perfectly aligned.
- Requires an animation for every weapon & sight combination.
- Only requires a single camera.
Multiple cameras:
- Easy to line up with sight.
- Requires no additional animations.
- Requires an extra camera for every weapon & sight combination.
Math:
- Once you’ve figured out the math, lining up the sight is easy.
- Requires no additional animations.
- Only requires a single camera.
- Support any weapon & sight combination you can think of.
You can read a similar thread here: How to make aiming?
Includes a post about multiple cameras and a post from yours truly pointing to an true first person demo I did using the UDK, as well as a run down on the math you can use to line up the camera with the weapon sight.