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Offline Parrott-Cannon

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Postal Shoot Error
« on: May 19, 2011, 08:02:46 AM »
How far does the muzzle have to be from the correct sight line to cause a given strike error on the target?  How does barrel length impact the error?  The attached graph provides the answers to these questions using the postal shoot rules.  Hope this helps those participating on this years postal shoot.

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Offline Double D

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Re: Postal Shoot Error
« Reply #1 on: May 19, 2011, 10:01:49 AM »
I got my head around this.

You have the rear sighting plane and the  front sighting plane.  The difference between front sighting plane and rear sighting plane is called the sight radius.  If you have a 12 sight radius  and your shot strikes   9 in high you need to lower the front sighting plane .012 inches to hit center.

Or you can raise the rear sight plane .012 inches for the same effect.

Is that correct?
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Offline dan610324

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Re: Postal Shoot Error
« Reply #2 on: May 19, 2011, 10:03:52 AM »
must be so
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better safe than sorry

Offline Parrott-Cannon

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Re: Postal Shoot Error
« Reply #3 on: May 19, 2011, 10:51:44 AM »
Maybe this picture will explain the graph.  Think of it as looking down on the cannon.  If I am off by blank (muzzle error) inches from the correct sight line what effect does that have on the point that the projectile stikes the target.

 

That is of course way we have sights on guns.  It is remarkable that the eye can align a short barrel as well as we do.
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For a people who are free, and who mean to remain so, a well-organized and armed militia is their best security. (Thomas Jefferson)

Offline Parrott-Cannon

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Re: Postal Shoot Error
« Reply #4 on: May 19, 2011, 10:54:59 AM »
Quote from: Double D on May 19, 2011, 10:01:49 AM
I got my head around this.

You have the rear sighting plane and the  front sighting plane.  The difference between front sighting plane and rear sighting plane is called the sight radius.  If you have a 12 sight radius  and your shot strikes   9 in high you need to lower the front sighting plane .012 inches to hit center.

Or you can raise the rear sight plane .012 inches for the same effect.

Is that correct?

Yes; Thank you for your clarification in appropriate terms.
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For a people who are free, and who mean to remain so, a well-organized and armed militia is their best security. (Thomas Jefferson)

Offline keith44

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Re: Postal Shoot Error
« Reply #5 on: May 19, 2011, 12:42:14 PM »
hmmm, 3 inch impact error using 12 inch sight plane radius calls for 20 thousenths of an inch change in elevation... wow this is gonna be tough
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Offline Double D

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Re: Postal Shoot Error
« Reply #6 on: May 19, 2011, 01:19:37 PM »
Quote from: keith44 on May 19, 2011, 12:42:14 PM
hmmm, 3 inch impact error using 12 inch sight plane radius calls for 20 thousenths of an inch change in elevation... wow this is gonna be tough

No it's not, its easy, even easier than you think.  Read this post: Aiming a Cannon without sights, South African style

Basically if you hit 12 inches above your point of aim, then aim 12 inches below you point of aim.
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Offline keith44

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Re: Postal Shoot Error
« Reply #7 on: May 19, 2011, 09:15:48 PM »
cannonballs (lead spheres of appropriate diameter) have arrived, now for the shooting platform, and some practice shots.  Perhaps as long as one does not over analyze the aiming it is easier than it seems. :)
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