That:
http://www.x-fire.org/vsr10/mars/e.mars.html
Made for VSR-10,
Might not fit right away on the ARES.
I don't have that ARES rifle, but found some reviews on French websites.
Basically it was saying that the rifle is really good, but you have to take it apart to make sure everything is fine.
The one I saw in the reviews had the plastic feeding mechanism splitting under the pressure of the screws. Fix is simply to remove it, clean and superglue both halves properly.
The other thing is it seems that the stock cylinder is not that great. Any VSR-10 cylinders will fit.
On the plus side, aluminum piston and spring guide, 90° sears and top-notch external finish.