Can someone clarify once and for all how projectile damage relates to distance traveled?
All weapons lose damage over distance, though it depends on the actual weapon on at what range they reach their minimum damage.
This PS2 Weapon Data Sheet gives the minimum damage distances of all infantry weapons. The damage in between degrades lineary, i.e. every meter decreases the damage by the same amount until the minimum damage is reached.
In general, TR weapons have the shortest range at which they do minimum damage, NC weapons have slightly higher range and VS weapons have the highest range by quite a big margin but also the lowest minimum damage. However, there are exceptions to this, so you should look at each weapon individually.