I found this article on the Warlord site very good. I always greatly curtail weapon ranges from their theoretical maximum when designing rules. Typically, I use 25% of maximum effective range. My only quibble with this article is that the term effective range IS defined: it is the distance at which an average marksman has a 50% chance of hitting a man-sized target. What is an “average marksman” can be determined experimentally on a range. In any event, the rated maximum effective ranges of modern weapons are determined in this way.