Just cleaned up my BSA CS .177 air rifle, re lubed, seal change ect....Shoots better now but it has a rather loud twang when shot. I have heard that adding a piston sleeve can solve this problem. Does anyone know where I could get one? The rifle is one that has two main springs (which I dont know why, surely just one long one like the other BSA's would be cheaper). They are the original springs the rifle came with from the factory, even has the BSA logo stamped onto the spring, though faded.