It's supposed to be C to C at the muzzle, but I measure C to C at the breach & take off 1-2 mm,
you will never get more than "ballpark" accuracy because your velocity is going to be, at best, the average from your testing, but I find Chairgun is usually within "human error" level of accurate.
p.s I couldn't plot anything close to the .66" drop at 45yds that he claimed, but good luck trying
you need; scope height, pellet weight, velocity, zero range, pellet profile, bc.![]()