Help with Chairgun Pro

[Notimeman]

I'm trying to use Chairgun Pro. I enter my data:

Velocity = 900 fps with my Taipan Veteran .25

Projectile - GA (drag coefficent)

Pellet weight = 25,39 (JSB)

Scope height = 2.75"

Zero range = 50 yards

BC = .038 (from Hardair Magazine)

Scope = 10X



Chairgun says POI at 75 yards is 1.55 mil dots (actual is 1.0 mil dots) 

Chairgun says POI at 100 yards is 3.55 mil dots (actual is 3.0 mil dots)

Chairgun says POI at 150 yards is 8.84 mil dots (actual is 7.0 mil dots)

I have tried adjusting the BC in the program to see if I could get the holdover to match what I actually saw, but no luck.

Am I looking at this incorrectly? Any help would be greatly appreciated.

 

[PerkyVal]

Is your scope true mil at 10x ?

 

[davecole]

You are on the right track IMO. Adjust the BC to match your POA with the POI. You might find varying the velocity a wee bit will also help.

I’ve experienced the same thing and in more than one gun, mainly .25’s. 

BC is sometimes a FWAG. Depends on barrel twist, weather conditions, air density etc. BC as advertised is merely an adjustable variable. It is not a hard-fast number.

At the end of the day, it doesn’t really matter what the numbers are as long as your results are predicable.

The one caveat is: you have to achieve the same results at different distances. (I know, duh)

Example: chairgun says 50=zero; 75=1 dot; 85=1.5; 100=2.5; 125=4 dots etc (hypothetically speaking of course) Your results HAS to be the same with only possible shooter error as the variable. 

Toooooo many guys want the math to make the gun work. Nope; Make the gun work the math. It’s easier.

 

[SDellinger]

Same thing happened to me. I changed the scope power untill Chairgun matched what I was actually shooting on the target. I finally had to put 8.3X into Chairgun to get a match. I shoot on 12X. Don't ask me why it just worked. Have fun, Scott.

 

[fishinwrench]

Your chronograph is lying to you.

Shoot at different distances both closer and further away than your zeroed range, and measure your POI.

Next adjust your velocity data in chairgun until the chart matches your real world POI. 

The remaining chart data will then be as accurate as you will ever get it, and this will also reveal what your actual muzzle velocity truly is.

The math is good if the input is correct. Chronographs (even the good ones) are junk IMO. (unreliable at best).

 

[AnimalHitman]

It sounds like you have a variable power FFP scope that is set on 10x. That is the power to be entered into Ind Mag. Your max mag should be entered into Cal Mag.