I have decided to have a play with my Challenge and attempt to get more shots from it. I think it is using too much air per shot and this also shows up as being a bit on the loud side! My thinking is to reduce the size of the firing valve air chamber. (don't know what else to call it, but someone will know the correct term) I'm not to sure of the volume of the chamber, I guess the way to measure it would be to fill it with water and measure that, but I don't want to do that just yet. To start things off, I have inserted a plug into the 8.5mm drill hole that is at the bottom of the chamber and by measuring the plug, it will give me a 1.5 ml reduction, not a lot, but it does seem to have quietened the shots down a tad, so I'm hopefully on the right track. What I'm hoping for, is that one of the Steyr guru's has already done this and can offer some advice. Any thoughts?