20 MOA rail, Taipan...
 

20 MOA rail, Taipan Veteran, Chairgun  

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Joe
 Joe
(@jp_over)
Joined: 2 years ago
Posts: 34
2018-04-14 22:21:02  

Friends,

Are there any special considerations to enter in Chairgun such that it will adjust for my 20 MOA rail when calculating my range card/ballistics?  Is this even necessary?  I understand the concept (below pic) but am a bit ignorant on the application.

View post on imgur.com

Thanks!

Joe


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Joe
 Joe
(@jp_over)
Joined: 2 years ago
Posts: 34
2018-04-15 06:16:18  
Posted by: DomingoT

When a ballistics system ask you for the scope height as an input parameter, what it really wants is the distance between the scope axis and the gun muzzle. This is because the ballistic system computes the trajectory starting at the muzzle. Since this distance is not known, you proxy it (imperfectly) by measuring the distance from the center of the scope rings to the axis of the bore.

When you mount the scope at an angle, you can account for this by correcting the measured scope height.  You measure the scope height as you normally would, and then subtract from it the amount L*20*0.000290888, where L is roughly the distance from the muzzle to the scope body, 20 is the MOA correction of your mount, and 0.000290888 is the value of one MOA in radians. For example, if your measured scope height is 2 in and L is 25 inches, you would enter 1.85 inches instead of 2 inches in your ballistics system. The length L should not include the length of the moderator.

This gives you a first cut, the scope height is more like a parameter you infer to get the right elevations at short distances.

That is very helpful; thank you!

Joe


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ecolwell
(@ecolwell)
Joined: 2 years ago
Posts: 1
2018-04-15 06:58:34  

link and method

Chairgun and “Scope Height”

 


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zx10wall
(@zx10wall)
Joined: 2 years ago
Posts: 45
2018-04-17 08:18:49  
Posted by: DomingoT

When a ballistics system ask you for the scope height as an input parameter, what it really wants is the distance between the scope axis and the gun muzzle. This is because the ballistic system computes the trajectory starting at the muzzle. Since this distance is not known, you proxy it (imperfectly) by measuring the distance from the center of the scope rings to the axis of the bore.

When you mount the scope at an angle, you can account for this by correcting the measured scope height.  You measure the scope height as you normally would, and then subtract from it the amount L*20*0.000290888, where L is roughly the distance from the muzzle to the scope body, 20 is the MOA correction of your mount, and 0.000290888 is the value of one MOA in radians. For example, if your measured scope height is 2 in and L is 25 inches, you would enter 1.85 inches instead of 2 inches in your ballistics system. The length L should not include the length of the moderator.

This gives you a first cut, the scope height is more like a parameter you infer to get the right elevations at short distances.

Sweetness...........Thank you for sharing this. 


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Joe
 Joe
(@jp_over)
Joined: 2 years ago
Posts: 34
2018-04-17 14:18:52  

"... roughly the distance from the muzzle to the scope body..."

DomingoT - quick question for you about the above highlighted instruction.  Is the scope body measured from the center of the scope, objective lens, or the eyepiece?  

Thanks again!

Joe


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