There's just too many variables to determine how far sound will travel and be audible to different observers (or rather, "hearers" in this case?). Sound gets dissipated very differently according to terrain, density altitude (temp, pressure, humidity), wind condition, terra surface, etc. Gunshots also have different combinations of frequency and intensity depending upon caliber, pressure, barrel length, etc. For example, it could be quite possible for a 45acp to have the same pitch/frequency as a 12ga shotgun, but the 12ga could be considerably higher intensity, aka louder so the pistol would sound identical to the shotgun if it were fired closer. A 30-06 at a mile away might sound similar to a 9mm at a quarter mile.
There's a lot of science you can tie to this to locate a sound based on echoes or transmission time between multiple spread points, and the relative volumes perceived at those locations, but by and large that's going to require intelligent software and a lot of intricate hardware. Not something you can do by ear.
Has there been research into this? Yes, and there are lots of technologies out there that have databases of different gunshot profiles, correlated against disturbance patterns for wind, terrain, and surface effect distortions, etc etc - in other words, it's a known art. Is it something you can do 'by ear'? Nope.