I just use the regular 12fpe Vortek spring kit and tune it with pellet weight. I am pretty new in this game but I am going to make a statement I believe in but it will make some unhappy. But here goes. Quit blaming the gun, the spring, the scope, the mounts, the weather, the grease, the shims, and learn how the gun wants to be shot. I am referencing bench shooting. These guns are very very touchy. They require absolute consistency. It's not easy, it's hard. You need to make it muscle memory. Chasing phantoms within the gun is not the answer. You can only do so much. It's the Indian not the Arrow 99 percent of the time. Pellet lots very. If the gun shoots until you buy your next lot of pellets then goes haywire, it doesn't like that lot of pellets. Try some other pellets of similar weight.Check the velocity to see if something is going on with the gun. But number one.....learn to shoot the gun.