I have a spyder RT and out of the box I can't adjust the velocity any higher than 250fps. I tried a stronger spring, but it won't shoot unless I loosen the velocity adjustment screw. It strange. If I tighten it too much the bolt won't stay in a cocked position. If I loosen it until it locks, but still fires, the speed is even lower. If I loosen it a little more, I can get about 270fps, but that's about it. Help!