The barrel band designon the Discovery (and other 22xx Crosman designs) is such that when the two set-screws are tightened on the barrel band, the barrel and airtube s are squeezed together.
This has the same effect as a "drooping" barrel on a springer: You culd run out of "up" adjustment on your scope, the barrel is under a downward tension, and most important (to me!) is when a barrel extension is added (like the TKO brake) the barrel center line is angling downward and encroaches into the space needed toattach the fill adapter and fill the gun.
The solution is to either shim the barrel and airtube away from each other, or add set screws to the barrel band to separate the barrel and keep the breec h (which is the scope mounting point) and the barrel in line, and parallel to the airtube.
Shim by loosening the barrel band set screws, cutting 4 pieces from a soda can about 1/2" X 1/2" and forming 2 of them to the radius of the barrel and 2 to the radius of the airtube. Slip one or two of the shims UNDER the barrel between the barrel and baelband and one or two shims OVER the airtube between the airtube and barrel band. When in place, gently tighten the set screws. Too tight and you will undo the work you accomplished by shimming.
A much better and stronger way is to drill and tap 4 additional set-screw holes on the sides of the band ... 2 angling upward to the barrel and 2 angling downward to the airtube. This triangulates the barrel and airtube mounting and makes for a very sturdy barrel mount. It is tricky to drill the angled holes on the flat sides of the band. I use a stub mill to mill a flat for the drill bit to work on. Not sure if I can attach a pict of a drilld band but here is a try:
Pict of a drilled band on a pistol:
http://www.tko22.com/TKO_gallery/images/drilledBand2260BR.jpgClose up of band:
http://www.tko22.com/TKO_gallery/images/drilledBand.jpgNote the two set screws on each siide ... one angling upward and one angling downward.
With the barrel parallel to the airtube like it should be, it's easy to attach and fill the discovery.
AND I am totally convinced throough lots of testing that the drilled barrel band is the most reliable way to increase acuracy of the discovery rifle. Better than all other barrel work combined.
Have a great week!
MIke T.
p.s. Adding another barrelband that isn't shimmed or drilled makes the situation worse. For a hunting gun, I recommend 2 drilled bands for best "ruggedness".
