Modern firearms, despite the massive amounts of effort put into their design and construction, still exhibit inherent inaccuracies and will in the future. The question this thread asks is how large these dispersions are for modern firearms, how this compares to current weapon setup and how the weapons may be changed to more realistic behaviour.
The accuracy of firearms is measured in arcminutes (generally printed as MOA, or Minutes of Angle). 1 MOA at 100 yards is about 1 inch. (1 MOA at 100 meters = 2.908 centimeters.) The question to be answered now is, how accurate are ingame firearms currently, and how far off are they from the real life counterparts. Below I am detailing what we need to know to figure out the shot group size ingame, and what I found out about real life weapons approximating the weapons ingame.