How much eye relief does one need when mounting a 4-15 scope on a power master 760?

That will depend on the scope and your eyes- but is ABOUT 3.5 inches. (Distance between your eye and the rear lens of the scope) It is the distance where you see the full image in the scope. You adjust it by sliding the scope forwards or backwards in the rings before tightening them down so that it fits YOU when holding the rifle in firing position. Please note- failure to pull a heavy recoiling rifle in TIGHT to your shoulder will result in a cut over your eye from being whacked with the scope.