Bret, I would not recommend using the shrink tube, it is a temporary fix, at best. When it starts to come off in pieces and it will, it makes a nasty mess inside the gun. I see that you also posted in the Gamo Gate, so I'll assume your working on a Gamo. The best thing to do is make, or have made a custom fitted guide and top hat. If that's not an option, the next best thing for a Gamo, IMO is to use a Crosman spring and top hat. The Crosman spring fits the rear guide pretty good and will take out most of the twang. Since the quality of the spring is not as high as the aftermarket springs, I would get 2 springs, 1 top hat and seal. Should be about $20 shipped, for all of it.