The GL-SHOCK does not make a noticeable difference in felt recoil to me, simply because I don't really think about the recoil with a 5.56.
It does make a noticeable difference muzzle rise - the sights stay on target better with the GL-SHOCK. I can shoot slightly faster accurately with the GL-SHOCK at a given range than I can without.
As the caliber increases, the benefits are more noticeable. It totally changes the way a 7.62x39 AK recoils - it comes back instead of up, and the recoil feels softer.
It makes a noticeable difference on shotguns, and with a .50 Beowulf I was able to watch my impacts through the optic (unmagnified) at 100 meters.
On a precision rifle, there are a couple things to think about. If your eye relief is very close and you tend to crowd the scope, it might help contribute to a black eye.
Also, some people will compress the spring a bit while precision shooting. these people may se a slight widening of their groups due to allowing the spring to push the rifle forward while the bullet travels down the bore. (same concept as using muscles to hold the rifle on target - there is a natural relaxin of the muscles when the trigger breaks.) Also, if the spring is compressed, there may be some bounce in the rifle as the bullet moves through the bore. Some people see no issues with precision shooting and some notice a difference, so I believe it is based on the technique of the individual shooter.
