Hey man, don't worry too much about range of motion. If you do the prescribed PT and really work on breaking up the scar tissue in the first 6 months after surgery then you should be fine. I have broken my index knuckle, same as yours, on my right hand 3 times and had it pinned twice. I have lost about 2% of flexion but as far as pulling a trigger or dexterity in that finger, it's perfectly fine. I shoot quite often and my occupation entails lots of fine motor functions and my finger has never bothered me. Hope this helps to alleviate some of your anxiety!