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 Post subject: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Tue Sep 22, 2009 10:37 pm 
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Every time we shoot at something, we create a sight picture. A sight picture consists of three points, the eye, the muzzle (or front bead) and the target. This alignment of these three points comprise the point of aim (POA). We know however, that a shotgun is rarely aimed; rather, it is usually pointed.

The point if impact or POI describes where the center of the pattern will be given a certain point of aim. It is the relationship of the POI to the POA that shooters deceive when they say they want a certain POI.

Trap shooters usually want a high shooting gun, a high POI to avoid having to cover rising targets with the barrel; less so with skeet shooters and lesser still for sporting clays shooters who often want guns that shoot flat, meaning that the POA and POI are the same.

The POI is determined by where the barrel is pointing when a POA is created as we point at a target. Well, obviously, right? Well, no; it's not always obvious. I wasted years demonstrating that fact (low cheekbones, looking down at the rib, shooting over everything without realizing it).

Example: hold your gun with the butt near your waist. Carefully create a sight picture - align your eye, the muzzle and a target across the room. (The butt remains near your waist.)

The sight picture is perfect, right? Right; your eye, the muzzle and the target perfectly aligned. If the gun is fired, will you hit the target? No. Why? Because the POI was vastly different from the POA. The eye was above the rib, far above in this case and that made the POI far different from the POA.

This is an important concept. It is the eye's position relative to the rib that determines a gun's POI. The POI changes as the position of the eye relative to the rib, changes. Raise the eye and the POI rises. Raise your head during a swing and you shoot over the target.

Swing in the direction of your gun mount at a hard angle target (to the right if you shoot right-handed) using your forward hand to move the gun and you will probably shoot behind it. You probably moved the comb away from your cheek, which moved your eye to the left of the rib. The target was traveling to the right so you shot behind it.

This is why consistent gun mounts are so important. (Practice at home with an empty gun.) Consistent gun mounts promote the eye's remaining aligned with the rib during swings. The eye must not move out of alignment if you want the POI to be the same as it was when you patterned the gun. (You did pattern your gun for POI, didn't you?)

Things that help keep the eye aligned with the rib in addition to consistent gun mounts (same place on the shoulder), include good body posture (natural and upright), a correct stance (able to swing far enough but not too far) and a gun that fits (has stock dimensions that allow a good shooting form to be used). If a gun doesn't fit, one or more elements of a good shooting form will be corrupted.

Do everything you can to assure your eye stays aligned with the rib with the same alignment it had last time you shot, last target, last squad or last week.



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Rollin

Author of "Stock Fitter's Bible, Second Edition," which explains the interrelationships between shooting form, stock dimensions and a shooter's size and shape http://www.amazon.com/Stock-Fitters-Bible-Second-Edition/dp/1451570384


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 12:38 am 
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Thanks Rollin, great post for me. It amazes me how often i need to be reminded these basic principles. It's almost a given that when i have a sub par day, it comes down to lack of basic fundamentals, not some great mystery.

Who was it that said head on tha stock, eye on tha rock?


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 1:08 am 
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You certainly have the right idea, Rollin.
I always want shooters to be satisfied with their results, and poor alignment (for any reason) is a fundamental condition that can be corrected to improve every shooter's score.
I rarely work with wood to a major degree these days, since I am tied into making the metal parts (barrels, chokes, mechanisms) work better or be better aligned for shooters.

The crooked choke tube hole, and to a lesser extent, the improper machining of a tube are the two most common reasons for a shooter to fail in their attempts at excellence when they have an otherwise reasonable fit of the stocks.

However, a straight choke will not let a poor fitting gun get over the lack of shooter-to-gun alignment, any more than a perfect fit of stock will make up for a mis-aligned choke. The two situations complement each other and the shooter cannot count on the best results without the minimum of alignment deviance in all critical aspects.

There are some who recommend the spacer shim adjustment available with some models be used to correct improper impact, but I would prefer that those shims be used to make a proper fit and sight picture first. If the impact is off when the eye/rib/stock alignment is spot on, then the choke alignment should be corrected as a better choice than to deviate the eye/rib/stock alignment to "correct " for a angled choke hole.
Doing so would not make any more sense than having a car with a front-end alignment problem be "corrected" by re-mounting the steering wheel in a different position rather than fix a fundamental flaw in the suspension and steering system.

Making do with a fixed and average stock that fits poorly is no better than being forced to use a car seat with no adjustment and locked in a cramped position.

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Article 3 pictures improper or dangerous choke installations, article 1 has explanatory illustrations, and article 2 has info. about bore/forcing cone improvements/limitations.


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 8:27 am 
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Joined: Thu Feb 26, 2009 4:32 pm
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Location: Utah
Rollin - should the comb be parallel with the rib? I have an adjustable comb on my 1100. I shoot it well, but my cheek will still hurt sometimes. I measured the comb last night and drop at front of comb is about ¼” higher than the drop at heel of the comb. Maybe the comb should be parallel with the barrel instead? I think I have the pitch set Ok. The stock in not a Monte Carlo, just the remington straight stock with an adj comb cut in.

Thanks


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 9:19 am 
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Rollin... Awesome post... I will keep this one in my back pocket....

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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 10:52 am 
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Squeal wrote:
Rollin - should the comb be parallel with the rib? I have an adjustable comb on my 1100. I shoot it well, but my cheek will still hurt sometimes. I measured the comb last night and drop at front of comb is about ¼” higher than the drop at heel of the comb. Maybe the comb should be parallel with the barrel instead? I think I have the pitch set OK. The stock in not a Monte Carlo, just the Remington straight stock with an adj comb cut in.

Thanks


Squeal,

You have a rising comb, which is common on field stocks/guns. The popularity of parallel combs is common on trap guns and is growing in popularity for skeet and sporting clays shooting.

The benefits of a parallel comb include no higher portion in the front that can be driven into the cheek during recoil and a consistent distance below the rib that allows an occasional sloppy gun mount without changing the gun''s POI.

If you can raise the back of the comb to make it parallel with the rib and still position your eye at the preferred height relative to the rib, I suggest you do so.
If you can't get it quite high enough in the back, making it closer to parallel is better than no adjustment at all in my opinion.

If you still feel occasional "cheek slap" and you're sure the pitch on the stock is correct, I would suspect that you are raising your head slightly during swings. That would cause the comb to impact your cheek instead of pushing it during the barrel rise that accompanies recoil.

_________________
Rollin

Author of "Stock Fitter's Bible, Second Edition," which explains the interrelationships between shooting form, stock dimensions and a shooter's size and shape http://www.amazon.com/Stock-Fitters-Bible-Second-Edition/dp/1451570384


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 11:00 am 
Field Grade

Joined: Thu Feb 26, 2009 4:32 pm
Posts: 87
Location: Utah
Thanks!!!! as I expected

Rollin Oswald wrote:
Squeal wrote:
Rollin - should the comb be parallel with the rib? I have an adjustable comb on my 1100. I shoot it well, but my cheek will still hurt sometimes. I measured the comb last night and drop at front of comb is about ¼” higher than the drop at heel of the comb. Maybe the comb should be parallel with the barrel instead? I think I have the pitch set OK. The stock in not a Monte Carlo, just the Remington straight stock with an adj comb cut in.

Thanks


Squeal,

You have a rising comb, which is common on field stocks/guns. The popularity of parallel combs is common on trap guns and is growing in popularity for skeet and sporting clays shooting.

The benefits of a parallel comb include no higher portion in the front that can be driven into the cheek during recoil and a consistent distance below the rib that allows an occasional sloppy gun mount without changing the gun''s POI.

If you can raise the back of the comb to make it parallel with the rib and still position your eye at the preferred height relative to the rib, I suggest you do so.
If you can't get it quite high enough in the back, making it closer to parallel is better than no adjustment at all in my opinion.

If you still feel occasional "cheek slap" and you're sure the pitch on the stock is correct, I would suspect that you are raising your head slightly during swings. That would cause the comb to impact your cheek instead of pushing it during the barrel rise that accompanies recoil.


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 11:30 am 
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Rollin you crazy old fart!! :wink: EXCELLENT POST :D You still have a vast amount of knowledge to share, thanks.
Great break down and explanation.
DD


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 11:33 am 
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DD,

I'm not that old.

Rollin


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 1:52 pm 
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Last year for my 60th birthday my wife bought me a Krieghoff K80 Super Schroll.

I have never shot the thing well. It has beed a long year.

A lot of the guys told me that it would take a year to get used to the K80.

This weekend one of the guys told I shoot way better than I have been.

I was told that I have not shot good since I got the K80.

He ask me if I had shot it on a pattern board and I said yes at 35 yards mounted.

When ask if I had done POI I said no.

We were off to the pattern board and I found out that it was 6" left and 8" low with IM at 25 yards!

I will never shoot a shotgun without doing that again.

If you shoot a shotgun be sure to shoot a few POI test!!!

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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 2:04 pm 
Field Grade

Joined: Thu Feb 26, 2009 4:32 pm
Posts: 87
Location: Utah
How did you fix shooting to the left? Move the comb so the Beads dont align?


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 3:27 pm 
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KRIEGHOFFK80,

An increasing number of shooters are realizing that just slightly different stock dimensions and balance can affect how well they shoot. It is unfortunate that shooting a gun before buying it is so problematic, if not impossible.

Squeal,

I would first suspect a problem with a screw-in choke if your gun has them. I would suggest you first confirm that it is the gun that is shooting left and not you. Shoot it from 13 yards using a rest and aim it like a rifle with a smooth trigger pull. If it shoots consistently to about the same place, suspect the choke(s).

It is also possible that the barrel is bent. If you can, look through it from the breech and see if the rings are concentric. If they aren't, the barrel is bent ( but can be straightened).

Briley and maybe others can make choke tubes to move the pattern. Eight inches should be simple for them.

Moving the comb would be my last choice of ways to correct the problem.

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Rollin

Author of "Stock Fitter's Bible, Second Edition," which explains the interrelationships between shooting form, stock dimensions and a shooter's size and shape http://www.amazon.com/Stock-Fitters-Bible-Second-Edition/dp/1451570384


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 3:48 pm 
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Rollin Oswald wrote:
KRIEGHOFFK80,
It is unfortunate that shooting a gun before buying it is so problematic, if not impossible.


My god... that is soooo true (that it is unfortunate)

It's like buying a car without test driving it or marrying a woman who is a complete stranger to you....

I personally think each new gun sold should have photographs of test patterns to prove that it's not worthless...

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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Wed Sep 23, 2009 4:51 pm 
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The funny thing about these threads to me is no matter how much explaining there is it still comes down to two converging lines. We know that two true parallel lines will never meet. And because we can not look down the exact center of the barrel two converging lines is the only way POI can hit POA. So with physics being what they are longer neck people are going to be at a disadvantage. The closer your shooting eye is normally to the point at which the butt of the gun rests at your shoulder the easier it is to build a gun with less dramatic angles in these converging lines. Increase the drop at heel to raise the rear of the receiver and you increase the muzzle lift and start getting cheek slap or shoot way under everything. Raise the comb to meet the cheek and you increase the angle of line of sight and make a smaller area that the two converging lines are close enough to hit anything. Until they have holographic targets that track the exact distance of your personal measurements above the actual target I don't see a fool proof solution. Putting the shot on the "X" is always going to require a certain amount of compromise somewhere. I guess striving for perfection should be everyone's goal but attaining it may be another story.


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Thu Sep 24, 2009 6:54 am 
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PhilG,

Your points are valid but the affect of a greater drop at the heel on barrel rise and cheek slap may be a bit overstated. It requires quite a bit of drop at the heel to cause cheek slap, probably well in excess of three inches.

As you wisely point out, shooters have necks, problematic necks, no less. (Many years ago I flew with a classmate who did not have a neck. He would have made a very good trap shooter providing he had enough cast in his stock to prevent his having to turn his head to align his eye with the rib - he couldn't do that.)

Another less troublesome problem most of us have is shoulder width. The shoulder pocket is waaay out there, nowhere near our eye. It increases the need for cast, turning the head and a stance that inhibits swing in the direction opposite the side on which the gun is mounted.

You wrote, "I guess striving for perfection should be everyone's goal but attaining it may be another story." Maybe not. With rapidly expanding knowledge of DNA sequencing and the rapid advances in genetic engineering (they can now engineer corn plants capable of moving to a sunnier part of the corn field under their own power, can't they?), how long will it be before parents can not only choose the sex, hair and eye color of their children but also design them to be outstanding shooters using DNA manipulation - severely handicapped in teen-mating rituals (another benefit?), but outstanding shooters.

I can see it now - headlines in a local newspaper: "Local eighth-grader breaks 1000 straight at Sparta to win HOA"

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Rollin

Author of "Stock Fitter's Bible, Second Edition," which explains the interrelationships between shooting form, stock dimensions and a shooter's size and shape http://www.amazon.com/Stock-Fitters-Bible-Second-Edition/dp/1451570384


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Thu Sep 24, 2009 8:00 am 
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It's funny you said "did not have a neck"! When I tried to describe myself that way once I was laughed at! :lol: :lol: :lol: :lol: :lol: But it's true! My "Adams Apple" is hidden under my jaw and my chin is below the line of my shoulders (more when I was in shape :roll: ).


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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Thu Sep 24, 2009 9:39 am 
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I just kept moving the comb to the right until the shot was in the center at 25 yards!

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 Post subject: Re: Point of Aim (POA) & Point of Impact (POI) explained
PostPosted: Fri Mar 04, 2016 4:37 pm 
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This topic was great reading. Thank you all for sharing your wisdom.




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