Donation

Support Equipment For PCP/HPA/CO2 and springers ,rams > Optics, Range estimation & related subjects

Chairgun estimation is SNAFU

(1/4) > >>

HOSPassassin:
OK. I know better than to take Chairgun's calculations as gospel, but this is ridiculous. Am I not accounting for something?

I am shooting a .177 caliber JSB 7.9 grain pellet at 938 fps at the muzzle. It averages 859 fps at 10 yards, which means it has a BC of .014, according to the PA website's calculator.

The weather conditions are 75 F, 66% RH, barometric pressure 29.85, and elevation 1000 ft. There is a slight breeze coming in at about 5 o'clock.

When all of this is fed into Chairgun, it predicts that if I zero at 17 yards, I should have a far zero at 40 and be .45 inches high at 30. I want a nice flat trajectory for as far as the gun's inherent accuracy, my abilities, and the cheap optics that I use will allow. I would be thrilled if I could hit within minute of squirrel at 40 yards.

So I zeroed at 17 and then took it out to 30, which is the extent of my range that is covered in shade ATM. The results were... interesting.

Granted, this gun is not fly-castratingly accurate and it may still be breaking in. However, POI was consistently 1.5 inches LOWER than POA. So much for .45 over.

This makes no sense. I'm not looking for perfection, just a reasonable level of predictability that I can interpret and adjust to.

Is Chairgun really that inaccurate for FAC power levels? I know it was developed in England. Is it primarily for use with UK-spec rifles? Do higher velocities make that much of a difference? Does it assume that you are using an Air Arms or similar-quality piece so that its general predictions will match what a finely made and adjusted gun will produce, rather than a mass-market piece like mine?

Is there some piece of relevant information that I have not included?

dan_house:
Scope height and pellet BC can/should be manipulated till the program spits out what you see on target

Trust, but verify :)

HOSPassassin:

--- Quote from: dan_house on July 13, 2023, 01:04:28 PM ---Scope height and pellet BC can/should be manipulated till the program spits out what you see on target

Trust, but verify :)

--- End quote ---

I forgot to mention: I did measure scope height and input it. I even used the chrono and worked out my own BC rather than relying on their default settings.

Struckat:
I have not tried a multi zero set up. I zero to top of the arc give or take a few feet, and the shoot to learn the hold over near and far.

CG is always fairly close, but then I don’t use it after the initial consultation for approx zero.

mr007s:
Try clicking on tool box in chairgun, open the caculate and calibrate window and pick caculate BC from poi at distance. Enter your site in range. Set a target at 40 with an aiming point at the top of your target but donot adjust scope. Fire 5 or ten shots at that aimpoint. Measure the drop and enter the numbers in the applet. and it will give you a BC but you probably need to adjust some .
For instance you have a drop e 10 inches. It the table it will list drop at 40 yards with the BC chairgun list. Play around with changing the BC to match what your actual shots were. You will be close so be sure and save the number in the pellet file. Also check that you have chosen the correct pellet profile, GA, G1 etc. The wrong one can screw things up.

Navigation

[0] Message Index

[#] Next page