I'd like to test my rifle out to see how much it will drop at longer ranges. Pacing off 100 yard increments isn't the most accurate way. I was thinking I could measure off increments of distance with a carpenter's tape, but that might take forever. I don't have a range finder yet. A GPS is only accurate to so many feet. I'd like to measure off at least 600 yards. Any ideas on this? Thanks for your help...