This is a great little gun. It's made for self defense not as a general target plinker. Mine hurt my hand as well, so I tried something new. I bought the biggest bicycle tube I could get at Wally World (1 3/4" or 2") and cut two (2) hand grips out of it. If you look at advertisements for commercial slip-over grips you can get an idea of the general design. Cut it with a box cutter or scissors then trim to fit. Wet the inside with some dish soap and water and slip it on the grip. When it's on good, put the second one over it. The reason for two is to make the grip just a little bigger AND to act as a shock absorber. You will be surprised at how much better it shoots and feels in your hand, plus the rubber of the tube makes it stay in your hand and now slip everywhere. The water/soap mix will dry quickly and the whole thing will be neat.
If you want to target shoot, get a bigger gun like an SR9 Ruger, or a Glock 17, or a Springfield XD9. Keep the Kel-Tek for self defense and practice with it as well. With the new grip you will think it's a different gun. Enjoy!