Yes you can fire 40 s&w in a 10mm auto. I didn't check accuracy, I just rapid fired about 13 rounds after two test fires with no problems through my glock 20. I imagine accuracy would suffer as there is an additional 0.140" of head space. A far as extractor wear, all it does is hold the cartridge as the firing pin hits it. Also when I loaded the mag I made sure every round was fully to the rear. I wouldn't do it every day but it can be done. A 10mm auto was designed to handle more than the 40 puts out anyway.