There are many ways to determine this, I guess. I'll share mine. I like to go off into the woods or mountains and hike with my hunting rifle on my shoulder. I'll spot a stump, or a notch in a dead tree, at 250-350 yards (by gusstimate,) Raise the rifle and fire. Use a tree or boulder to rest the forearm against if possible. Fire 5 shots. Now I get the range finder out and range in the actual distance. Then go down and measure the group size. WHOAA!!! My 1/2 MOA rifle/load is now a 4 MOA rifle load. Do this when you're hiking alone. It can be embarrassing!