If you want to buy the hammer don't let the installation stop you. It comes with instructions and is very easy to change. All you need is a small pair of external snap ring pliers which the instructions gives you brands and part numbers to buy if you don't already have one. I also needed pair of regular pliers because when I reinstalled the snap ring it wasn't as tight as it was beforeI removed it. But no big deal I just sqeezed it back tight with a regular set of pliers and good as new. My c-stocked M4 is now in compliance with 922r thanks to Kip, KZ & Geiselle but if and when a better trigger is released by Geiselle I will buy it. But for now this new hammer is a great product for us M4 owners.