Scope height and pellet BC can/should be manipulated till the program spits out what you see on targetTrust, but verify
Are you sure you were zeroed at 17 yards? Try zeroing at 30 yards. With your muzzle velocity THAT should be your zero! -Y
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?
Quote from: HOSPassassin on July 13, 2023, 12:31:40 PMOK. 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?LOL.....I found the same with my .177 cal recoiling springers and since I needed to shoot "real world" to verify "puter calcs" to get the real trajectories I just simply nixed the "ChairGun app" all together to shoot "real world" when getting a handle on the holdover/under for different setups and pellets!
How did you measure scope height? There a couple ways to measure but only one correct way.Go to this site and scroll down to "Chairgun and scope height".https://airgunaccuracy.wordpress.com/chairgun-and-scope-height/[/quote}I do it the way that the fancy UK shooter does it. I lower my magnification to the lowest level. I place a BIG + on a target. I get to point blank range of my barrel. making sure that I am level, I aim at the + in my crosshairs. The distance between the + and the pellet hole is what I use for scope height.Otherwise take 1/2 of your barrel dimension, 1/2 of your scope bell objective size, distance between bottom of scope and top of barrel. Most are between 1.5 anf 1.875 inches.Remeber that a higher scope height will look like a flatter trajectory. -Y