How accurate is the Chairgun App?

[Dr. Kralenstein]

As the title states, how accurate is this phone app?

I recently put together a 177 bottle gun and set it up for 30 yard plinking/bird pesting. Currently 12.7 fpe at the muzzle with cphp pellets. Chairgun says at my 30 yard zero, im down to 7 fpe already with these pellets. I checked the BC from HAM to come out to .012 which sounds about right.

Does this sound right? It's bleeding off over 5 fpe within 30 yards? I'm fine with that because it's still smacking the sparrows as I wanted, but I was curious if a squirrel was to come into view if it would be worthy of taking one. I'm not keen on maiming critters. I don't feel like 7 fpe would be okay unless it's a perfect head shot. Also, I just can't believe it drops 5+ fpe in such a short distance.

 

[davecole]

I use it and it’s as accurate as any other ballistic app available. The key to accuracy using it is, you have to enter the data points with some accuracy. Particularly the BC. The app uses a default BC but you need to enter the one for your particular gun and ammo and this requires a chrony and a reasonable distance to shoot.
Know the BC of your ammo is determined by your gun and how fast it’s shooting. BC is not a constant value and it varies.
If you use a BC you “found on the web” or a default value, it may not be correct for your gun/ammo thus, the accuracy of the app will be in default.
Chairgun will calculate the BC for you (there is a tab in the app under toolbox / calculation items where you enter the speed of your ammo at the two distances (30 yards apart will work, 50 is better if shooting long distances) and voila! You have an accurate and useful BC. Now also know, any time you change ammo or speed you have to repeat the same steps.
As for the energy part of your question, the default info, providing you are entering a close approximation of the speed, will be accurate enough for FPE.

 

[Dr. Kralenstein]

Ok, so when an ammo has the BC printed on its label, like FX slugs have, is that the given value I should enter in the BC section of the chart?

 

[dizzums]

my stormrider 177 at ~19fpe at the muzzle is good on squirrel to about 40 but its losing energy fast there .. i wouldnt try a 50 yarder unless it was a perfect profile headshot lol .. sounds like thats about where your at at 30 with 12 ..

 

[Dr. Kralenstein]

I went through the pre listed projectiles on the app and used premier lite which is what the cphp used to be called. It adjusted my values and it's saying I'm at 9.1 fpe at 30 yards which sounds correct. I figured there was no way it lost close to 6 fpe in 30 yards. I still won't use this one for squirrels. I have 22s and 25s for that.

 

[davecole]

Ok, so when an ammo has the BC printed on its label, like FX slugs have, is that the given value I should enter in the BC section of the chart?

You might try it and see. Input their stated BC in Chairgun. Making sure your zero is good. use two aim points; one near and the other far as far apart as possible (say, 15 and 50 yards).
Using the aim points as Chairgun suggest (clicks, mildots whatever you prefer) and fire at them. If the impacts are precisely what you used then the BC would be practical to use. If not then you will need to do your own BC testing.
Here’s an interesting read on BC testing from Hardair Magazine.

 

[Leon83]

always validate your bc.

it may change with velocity so it is recommended to validate you pellet trajectory.

 

[JungleShooter]

Good advice to validate the BC.

Here's the updated diagram of the previous post, Bob Sterne used a better ballistic engine, and a more precise drag function.


I like it that Strelok Pro ballistic calculator allows us to enter up to 5 different BC values (velocity dependent).

Matthias