I did mine on the cheap.Used an airarms s400 silencer adapter,10mm,it's a tight fit on the barrel.I removed the barrel by taking out the 2 screws that hold it near the breech and loosened the grub screw under the barrel at the muzzle end.I tapped the adapter on and put the barrel back in so far,gave the adapter some heat and burnt it in gradually until it reached the breech.Replaced the 2 screws and holder to clamp the barrel in and tightened the grub screw which gripped the barrel at the muzzle end and so trapped the adapter so it was solid.I put some tape on the adapter as I scratched it,I'll paint it sometime,maybe.
I'm a bit of a butcher but it works great,I also cut a slot in the overlever to fit a weaver rail for a red dot while I was at it.If you intend keeping the gun it's a cheap solution.
http://i116.photobucket.com/albums/o...n/P1120005.jpg