By effective range you are referring to what?
Total range: Depends on how good of a shot you are
Fragmentation range: See below.
Here is a section from the Ammo FAQ:
"Assuming true M193 or M855 ammo, velocity is the key. Velocity is dependant on barrel length and environmental conditions.
As barrel length increases, the bullet is propelled faster by the expanding gasses in the barrel, imparting more velocity on the bullet, resulting in a longer range until the bullet drops below 2700 fps. A shorter barrel has less range.
Temperature, altitude, and humidity are other factors. As temperature or altitude increases, air becomes less dense, and bullets travel faster. As humidity increases, air becomes denser, and bullets travel slower.
It is important, then, to keep in mind that any statistics given can only be approximate, and can be affected by a wide range of factors. But as a baseline, these numbers are what you could expect for 75° F, 25% humidity, at sea level, from various barrel lengths:
Distance to 2700 fps M193 M855
20” Barrel 190-200m 140-150m
16” Barrel 140-150m 90-95m
14.5” Barrel 95-100m 45-50m
11.5” Barrel 40-45m 12-15m
As you can see, barrel length and ammo selection make a major impact on fragmentation range."