I have had a number of conversations with guys on the phone that had "read" that the power adjustment on the Air Arms S400-S410 has a weakness in that it could be bumped of moved by accident thus messing up the way the gun was sighted in. As most of you know, the power adjustment knob is NOT a simple Hi-Medium-Low type of adjustment. It is a LOT more robust than that and works like a rheostat on a light switch in that you can turn the knob from full (22 fpe) down to 5 fpe and stop wherever you want. There are no "clicks" when you adjust the power. The knob just turns smoothly and you stop it wherever you wish.
BUT the rumors and reports are wrong. If you remove the stock (just a couple of screws) and look just about an inch under the power adjustment knob, you will see a hole with a small recessed allen screw. That screw allows you to "lock" the power adjustment knob so it can't move. So all a guy has to do is find the power level you want, then tighten the little allen screw and there will be no shifting, moving or altering unless you loosen the screw later and change the power yourself. Just thought I'd pass this tidbit along to set the story straight.