How do I calculate true muzzle velocity from my chronograph? If the readings are taken 6 to 7 feet from the muzzle how much velocity is lost? I'm trying to calculate drop at long ranges for a hunt I am going on. My range is only 150 yards and I want drop out to at least 400 yards. Not sure how much of a difference it would make but just want to be as accurate as possible with my calculations.