I've just picked a 420 up with the intention of reviewing it for AGW. Agree with the comments about the rifle being under rated. It really is a fine piece of kit and a looker to boot. It is worth fixing your model up as spares are as rare as hen's teeth. First target tests gave me 5mm groups at 7 yards standing in .177. One problem is the lack of info on these rifles. Will publish what I find.
John