Chairgun
Hi guys, I need some help here.
Which one is correct? Scope height and distance to target.
Is this the right way to meassure the height?
Set your scope to the minimum parallax adjustment distance and minimum magnification.
Cover the Objective lens with tinfoil and poke a very small hole (0,12″ or 3mm) in the center of the foil. (this will greatly improve the sharpness of the image at close distance and will allow you to see the cross on the paper at close distance)
Sight the cross on the yellow pages and with your muzzle as close as possible to the yellow pages fire a pellet.( I managed to get as close as one feet / 30 centimeters between muzzle and paper)
You can now measure from the center of your pellet hole to the cross you’ve marked on the paper.
This will give you your scope height for Chairgun.
Can I make it before I calibrate the scope?
Greetings
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So you calibrate your scope zero using your rangefinder. For example: lets say your want to set it on 25 yards. You set the target at 25 yards from your eye?
I measured center of the scope to center of the barrel and I measure distance to the target using my rangefinder… I am put my numbers into the program and bada bing I have my Centerpoint
There is two diferents questions on same picture.
A or B: scope height
1 or 2: how to measure distance to target
The pic he posted is blurry for me so if I’m to understand this correctly b is the measurement of where the scope sees after a few inches past the scope, which to me is way harder to find that measurement rather than center of barrel to center of scope.
A is the correct answer.
I use istrelok and in their FAQ they say to use scope hight and gave the website I referred to you…after getting my numbers for my scope and gun I input that into the software and bingo every shot is EXACTLY where the program said it would be.
If you saw the image, the height size, is dramatically diferent.
In Chairgun, this size, change the point of impact a lot. 1 inch changes the point of impact in 10 meters.
In all reality if your off by just a fraction I don’t see it being that big of a problem…unless your an inch off…but a fraction of a decimal isn’t going to change the poi dramatically
I read somewhere that the right height is B like for Chairgun but i dont know which one is the correct.
Scope height above bore at end of the barrel.
If you have an EDgun the rail angle is 0.5º (30MOA).
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Chairgun plots the TRAJECTORY of the pellet.
How high the front and back of your scope are above some random point along the barrel is IRRELEVANT, it matters where the pellet EXITS the barrel and it’s relationship to the centerline of the scope at that point.
If you are measuring distances with the scope, for something like field target, then the distance from the end of the scope should be used (the end of the GLASS).
Chairgun only gets you so far (I use it a lot more than most people who compete in field target), each rifle will have a different BC for each pellet. A JSB 10.4 grain pellet in 177 shoots different from my USFT than it does from my EDgun at the same velocity.
You will need to tweak the CG settings (BC and scope height) until the clicks (or holdover) in CG matches those you determined in the field (preferably in no wind, a tail wind will lift the pellet and a head wind will push the pellet down).
In order to find the centerline of my EDgun barrel to the bore I did the following; I measured from the underside of my scope’s bell to the top of the shroud (or barrel) then I moved back a bit (measured distance) to the tube and measured from the bottom of the tube to the top of the shroud (or barrel). Then I measured to the end of the barrel from one of both of the measured locations. Height above bore is half the scope tube/bell diameters, plus half the barrel/shroud diameters plus the measure gap. I then put all this into a cad drawing to verify my measurements show the 0.5º rail drop and then I drew the centerlines and found the height of the scope centerline above the bore centerline at the end of the barrel.
I have done this for four different rifles and it works great.
Once you get the system down you will need to set your zero at some given distance. Typically for Open FT I use a 30 yard zero. So to get set up for a match I shoot a 30 yard target and click up and down until my poi is right on for that distance (I shoot through a chrony to verify my velocity is what was figured for the click chart). Then I loosen the elevation turret and reset it to zero. Now all the clicks I figured in CG will align with what I am shooting that day.
I say that day because different temperatures and humidity levels will change the poi.
To check everything is on I shoot at 10 yards and then at 55 yards (the minimum and maximum distances for ft competition), if those distances work then i’m good to go.
If you REALLY want to go nuts create a click card for a bunch of velocities say 840, 850, 860, 880, 890, etc. That way you set the 30 yard zero then shoot at 55 and pick the click card that works best (this way you don’t have to verify the velocity).
There is another way to do it that is more accurate. Hans & Ray Apels have a method that measures the BC and drop at the same time. I watched them do it at the Nationals last year but have not done it myself (it has something to do with shooting at 20 yards and clicking up 1″ with a ruler on the target).