I hear a lot of people complaining about the ballistic software Chairgun not being in line with their real world results. But in my field target rifle and scope combo’s it has improved to being very accurate by measuring “scope height” in the right way. When I gave other field target shooters the advise to do the same thing they also find that Chairgun is very accurate. And that the input value for “scopeheight” was the parameter for which they had used the wrong input.
“Scopeheight” is a major affecting parameter in every ballistic calculation. Much more so than a few hundredths of BC or ten FPS.
“Scope height” is actually the wrong name for this parameter. The actual parameter needed is the difference between the line of sight and the center of the barrel at the MUZZLE. See the picture for the explanation of the difference.
The right way to measure this “scope height” is:
- Mark a cross on something like a Yellow pages or some other sheet of paper.
- Set your scope to the minimum parallax adjustment distance and minimum magnification.
- Cover the Objective lens with tinfoil and poke a very small hole (0,12″ or 3mm) in the center of the foil. (this will greatly improve the sharpness of the image at close distance and will allow you to see the cross on the paper at close distance)
- Sight the cross on the yellow pages and with your muzzle as close as possible to the yellow pages fire a pellet.( I managed to get as close as one feet / 30 centimeters between muzzle and paper)
- You can now measure from the center of your pellet hole to the cross you’ve marked on the paper.
This will give you your scope height for Chairgun. (Originally posted by Harry’s Lad, the programmer of Chairgun).
For me this improved Chairgun to the point that it is more accurate than I can shoot my groups. I use Chairgun for Field Target shooting from 8 out to 55 yards to make my turret tapes.
Of course you have to make sure your scope’s click values and mildot spacing are correct as well. My Big Nikko for instance did not have the 1/8 moa clicks that the turrets said. I measured them and they are 1/7th moa clicks actually.
(Pictures by Steve in NC from the Yellow Forum and Brian Samson from Shooting-The-Breeze original thread click here)