Choosing between a factory hammer and a bobbed hammer will depend on your choice of optics, or whether you even want optics. The factory hammer (the silver one on the right) is long and square with small indentations on either side. The square shape allows a hammer extension to be attached to it and secured with a set screw which engages one of the small indentations on the right or left side, depending on which side you decide to mount the hammer extension. If you are going to mount a conventional scope (one that overhangs the rear of the receiver, and therefore the hammer) then you will most-likely want the factory hammer and a hammer extension off to one side. This will enable you to manually cock the hammer. If, on the other hand, you choose a Scout scope, red dot, or to forgo the optics altogether, then you may want to opt for the bobbed hammer. I have shortened and rounded the rear end and chamfered the edges, prior to having it Cerakoted.