Originally Posted by blacklab
its critical to get center of barrel to center of optic right
That's the mistake most people make with the calculation.
Centre of optic to centre of barrel is NOT the measurement required for the ballistics calculation used by Chairgun and pretty much every other ballistics calculation apps available.
The measurement required is the distance between line of sight and muzzle, directly above the muzzle.
If you're measuring the height of the scope above the barrel, you're measuring the wrong thing. To be fair it's not a million miles off, but it isn't the right value to use and will give noticeable trajectory differences to longer range.
For this question though, the difference won't be noticeable because we're only talking about 10 yards.
Here's a little diagram to illustrate what I mean.. scope-height-measurement.pdf