The AAC-21 rail set is constructed from metal and fits quite well on of course the AAC-21 sniper rifle. I would highly recommend getting these rails considering they add to the modularity of your rifle in that due to their quick mounting and dismounting they can be easily moved and used to fit your needs. I personally use these rails for mounting lasers, an EOTech holographic sight (for closer enemies), and even occasionally a light. These accessories work very well on the rails due that they are a standard picatenney. I must say though they are a bit pricy even for their quality due that they are kind of small but you do get an included tool to mount them so its not to horrible.
Kind of needed for AAC-21 rifle, but for the rifle's price this kinda should of been in a package deal with it