Actually this is an issue that other games, mostly dealing with magic use, have had before. In those, spells would just be unusable within a certain range if they were meant to be long range. That obviously wouldn't work here. I laugh at all the "but physics says..." responses. How's this for an idea that can fit in the mythos. All snipers have elemental damage. Maybe some cunning gunsmith designed the sniper ammo to absorb light of its element as it was travelling through the air. The bullet would still be subject to rules of kinetic energy with a drop off if range got to far(I don't think there are any maps where this really comes up). The longer the bullet flew, the more energy it would absorb from light, thus inflicting more damage. How's that sound?