Thumper,
Here is a picture of an uncut Bisley adjustable butt pad laying on the butt of my HW55T. The base plate has just enough aluminum to cover the wood but the rubber pad comes up a little short at the toe. Depending on your taste that may or may not bother you. I've seen some high end adjustable pads that don't even come this close. Because the contour of the 55T at the butt is rather large, you don't have a lot of room to move the base plate around until you like how it fits. The top screw hole in the base plate may not line up with the top screw hole drilled in the stock and your only option will be to plug the hole in the stock and re-drill it to match the location of the hole in the Bisley base plate (I wish they'd provide these base plates without holes so we could drill them where we want them).
I've installed these pads on 5 or 6 of my air rifles. I try to match the top hole in the base plate to the top hole factory drilled in the stock. In every case the bottom hole in the base plate ends up being too low, i.e. too close to the toe of the stock, which could result in the stock cracking if you aren't very careful to use a short screw and drill a hole in the wood that matches the screw size precisely. Instead I drill a new hole in the bottom of the base plate to match the factory drilled screw hole in the toe of the stock This isn't a big deal as the pad always hides the empty factory hole left in the base plate (unless you adjust the pad UPWARD).
The Bisley pad will increase your LOP about 5/8 of an inch over the factory pad.
IMO an adjustable butt pad looks cool on any gun and in 90% of the cases improves the fit and feel FOR ME when I shoulder the gun. HOWEVER, the HW55T is a wonderful fit just the way it is and for me there would be no advantage to adding an adjustable pad. The effort to fit one would not be worth the return.
If you do install a new pad, any pad, make sure to drill the required holes and secure the pad to the stock before you do anything else. Then, following the contour of the stock, scribe a line around the pad to grind to (I use the back of the tip of a very sharp knife). You'll end up installing, checking, removing and grinding, installing, checking, removing and grinding. By drilling your holes first you assure that the pad will go on exactly the same each time. If you just hold the pad in place throughout this process THEN drill holes, the drill bit WILL wander and your perfectly fitting pad will not fit perfectly anymore.
I would speculate that your pad has pulled away from the toe of your stock because someone tightened the bottom screw too tight and cracked the inner hard plastic-like "back bone" of the pad (bottom picture). The screws are typically of the counter sink design (tapered under the head) and over tightening will crack this component. I had one that was pulled away slightly and after removing the pad and discovering the problem I was able to open the crack up enough to get Super Glue in it then secured the pad between two pieces of wood with a clamp so the pad flattened while the glue cured. Afterwards I reinstalled the pad with LIGHT screw pressure and you wouldn't know it was ever cracked.
