There's something not kosher with your rifle or scope if you can't get better than 3" groups with factory fodder, provided you know that you're capabile of delivering better groups
There are two points t be made here.One is that some loads do not work well in some rifles so if you have only tried one load there may not be a problem with the gun or scope .The other is that you never stated what size groups you shoot with other high powered rifles.This needs to be known to eliminate the possibility of flinching or shooter error.