I have no personal experiance with the 40 conversion,but a friend has a newer model 9mm(serial # 65000+) and bought a 40 conversion and has had no problems. I have only read the the older 9mm's that owners bought the 40 kits for had some problems and had to send there gun and 40 slide to kel-tec for proper fitting. There is a dealer in my town that has a older 9mm,(35000 range) with the 40 conversion kit only,(he sold the 9mm slide) that appears to be fired very little,if at all that i would love to buy,($200.00) but have wavered because I would want to immediatly send it to kel-tec and have them upgrade the slide to hardchrome and install night sites and perfect the funtion if not 100% already,but this with cost me anouther $100.00 that I don't have right now. Although now that I think of it i could buy it and hold off until I get the extra $100.00???.