Point of aim vs point of impact

[DShortt]

Do you site scope using a good rest ?

I think it's fine. It's not a well known brand but it has a cast iron frame, leveling feet, bubble level, forend stop, elevation adjustment and a bag on the top rest.

 

[skeeljc]

In Tony Boyer's The Book of Rifle Accuracy he talks about changing his POA from the center of the "moth ball" (the center circle) to the top of the moth ball. I doubt he ever used the square that is way above the rings. He does not talk about how far his POI is from his POA but I doubt it is very far.

If your rest and rear bag are not capable of repeating it will cause your group to enlarge. The further the distance between the POS and the POI the greater the chance to induce error.

 

[DShortt]

Yes, I think the last sentence is a better way of wording what I was trying to describe.

 

[Brians356]

What really jumps out at me is that your POA and POI are roughly 1/2". Often mine are 2"-3" different because I never stopped to think about the consequences of doing that. For example imagine your POA was the bottom point of the center triangle and your POI was the far right point of the center triangle. 3" high and 3" right. And you didn't adjust for it but shot a 5-shot group and wondered why your having difficulty getting under 3/4" of group size. THAT'S what I've been doing.

I get what you're concerned about. I agree if your POI is relatively far above POA, then the effect of any cant will be larger. With zero cant, no problem. But assuming there is a certain amount of cant (however small), and it varies slightly from shot to shot, the spread of displacements of POI due strictly to varying cant will have larger magnitude, contributing more to increased groups sizes than if your POIs were closer to POA. If the cant is non-zero but always exactly the same, shot-to-shot, there will be no increase in group size.

Since no human (leveling devices notwithstanding) can eliminate cant 100%, or can perfectly replicate non-zero cant shot-to-shot, in general it's better to have POI set relatively close to POA, to minimize the effects of cant on group size.
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[Sandstorm]

different

Not different.. whatever works for you is all that matters. Be consistent and aim small is
how i do it

 

[jelenko]

Is aiming for bottom of the V different than aiming for the center of the X? (Honest question, I think I know what you mean.)
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The bottom of the V is a smaller area that the 'middle' of the X => there's a better chance that you're aiming at exactly the some point with the bottom of the V vs the 'middle' of the X.

 

[Brians356]

Not different.. whatever works for you is all that matters. Be consistent and aim small is
how i do it

So you aim at the center of the X. Thanks, I thought maybe I was missing a finer point.
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[Brians356]

The bottom of the V is a smaller area that the 'middle' of the X => there's a better chance that you're aiming at exactly the some point with the bottom of the V vs the 'middle' of the X.

I agree! But apparently that's not what sandstorm had in mind. Or at least he chose not to say he did when I asked.
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[DShortt]

I get what you're concerned about. I agree if your POI is relatively far above POA, then the effect of any cant will be larger. With zero cant, no problem. But assuming there is a certain amount of cant (however small), and it varies slightly from shot to shot, the spread of displacements of POI due strictly to varying cant will have larger magnitude, contributing more to increased groups sizes than if your POIs were closer to POA. If the cant is non-zero but always exactly the same, shot-to-shot, there will be no increase in group size.

Since no human (leveling devices notwithstanding) can eliminate cant 100%, or can perfectly replicate non-zero cant shot-to-shot, in general it's better to have POI set relatively close to POA, to minimize the effects of cant on group size.
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I see. This is what I was thinking but wasn't sure if I was wording my thoughts correctly. At least now I'm confident that I've identified at least part of the trouble I've been experiencing.

Thanks to you and all who have replied. I appreciate more than you know.

 

[22BRGUY]

Spin drift is another possible consideration

 

[skeeljc]

I adjust my front rest so the horizontal crosshair is parallel to the horizontal lines on my target. Then I can see when the gun is not coming back into battery correctly (without cant).

 

[Sandstorm]

But apparently that's not what sandstorm had in mind

Apparently you did not read my initial comment.
I aim for the bottom of the V.....my answer was whatever works for you Brian because thats all that matters.

 

[David Milisock]

I'm a casual shooter and have been having troubles trying to improve my shooting and group sizes. I started a thread yesterday about anti-cant devices and one of the replies jarred something and I believe I've had a moment of clarity. I purposely do not shoot my point of aim so as to not loose it but I've never paid attention to how far the point of impact is from the point of aim. It's just occurred to me that it seems that the further the point of impact is from the point of aim then mistakes such as scope/rifle cant will be amplified. Is this plausible or no? I'd just go to the range and see for myself but as I'm still a slave to the grind that's not possible for a few days so I thought I'd see what some of you think. I'm betting several here know the exact answer so I'm looking forward to your replies. Thanks for looking.

There are MANY shooting disciplines and point of aim VS point of impact come into play many times. A perfect vertical alignment is a wonderful concept however it becomes impossible as distance increases due to wind and rotational drift.

If you rifle is perfectly level and your sighting mechanism plumb you can make lateral adjustments for drift and vertical adjustments for range with angle adjustments.

With that said in the field I can't seem to be able to find targets that sit still long enough for me to make sight adjustments. Critter, mid sized game, man or beast they just seem to make me work at it. If I'm lucky I can get a good target ranging but most of the times I get a general area ranging and in any case I then hold over, under, left or right.

A good stable and plumb sighting mechanism is required but the best advice I have for any shooting discipline and especially field work as it's a very fluid set of ambient conditions is PRACTICE!

 

[DShortt]

My shooting these days is off a bench @100 yds. I believe my problems center around 3 primary mistakes I have been making. First, I was using a single 1" orange Birchwood - Casey sticker on an 8 1/2" x 11" sheet of copy paper. This is not a large enough aim point to allow me to judge if I was inducing cant or not. Second, the first mistake is compounded by the fact that I was not keeping my POA and POI close together. Depending on the load combination I was shooting on any particular outing my POA and POI could be apart by as much as 3" high/low and 3" left/right. By doing this even small amounts of cant are magnified much more than if the POA and POI we're close, say 1/2" and 1/2". And third, while the scopes I have been using are fine for hunting or field shooting the magnification and clarify are not sufficient for precision shooting. When you consider that all of these mistakes tend to compound one another I feel confident that when I correct them I will see immediate improvement.
My plan for correcting these mistakes is to use a target sheet with horizontal and vertical lines to identify any cant, reduce my POA and POI to roughly 1/2" of separation and to upgrade to a true target scope to provide sufficient clarity and magnification so that I can clearly see the POA.
I did not come to these conclusions on my own, it was by the wisdom and experience of the members of this forum and I greatly appreciate all of the responses this thread has received. Thank you all very much!

 

[Brians356]

My shooting these days is off a bench @100 yds. I believe my problems center around 3 primary mistakes I have been making. First, I was using a single 1" orange Birchwood - Casey sticker on an 8 1/2" x 11" sheet of copy paper. This is not a large enough aim point to allow me to judge if I was inducing cant or not. Second, the first mistake is compounded by the fact that I was not keeping my POA and POI close together. Depending on the load combination I was shooting on any particular outing my POA and POI could be apart by as much as 3" high/low and 3" left/right. By doing this even small amounts of cant are magnified much more than if the POA and POI we're close, say 1/2" and 1/2". And third, while the scopes I have been using are fine for hunting or field shooting the magnification and clarify are not sufficient for precision shooting. When you consider that all of these mistakes tend to compound one another I feel confident that when I correct them I will see immediate improvement.
My plan for correcting these mistakes is to use a target sheet with horizontal and vertical lines to identify any cant, reduce my POA and POI to roughly 1/2" of separation and to upgrade to a true target scope to provide sufficient clarity and magnification so that I can clearly see the POA.
I did not come to these conclusions on my own, it was by the wisdom and experience of the members of this forum and I greatly appreciate all of the responses this thread has received. Thank you all very much!

For your purposes and equipment, you're cutting it too fine. If you are shooting groups any larger that ~1/2" at 100 yds at this stage, I would allow at least 1.5 inches between POI and POA. Just avoid having POI, say, 3 or more inches away. Any effect of cant variability will be "down in the noise level" if you are a couple of inches from POA at that distance. For hunting, you will eventually adjust your scope for a reasonable point-blank range by setting POI 3" high at 100 yds (to pick a common rule of thumb figure).

Don't be too quick to dismiss your hunting equipment. I've developed loads for several OEM sporters w/ mid-level hunting scopes that consistently shoot 5/8" groups off a simple bipod or cheap front rest/bag off the bench. What is your ultimate goal for group size, with the gun and scope you are working with?

Edit: I suggest you take a common 8" plastic "torpedo" level with you to level your targets on the backer. Then adjust your bench setup so the the reticle aligns with the target for each shot.
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[jelenko]

POA and POI could be apart by as much as 3" high/low and 3" left/right. By doing this even small amounts of cant are magnified

I disagree. If cant is consistent, there is absolutely no effect.
If cant changes a bit, the difference in POI is EXACTLY the same as if the POI and POA were the same.

Changes in elevation or windage will have exactly the same affect on the POI regardless of the distance from the POA.

The fact that changes in elevation and windage are not linear when the rifle is canted does not affect the POI just because the POA is different.

As mentioned, I regularly test loads with POI's that are 2 MOA away from the POA. Because I'm shooting from prone with a sling, I have a 10* cant to the left.

 

[Brians356]

I disagree. If cant is consistent, there is absolutely no effect.
If cant changes a bit, the difference in POI is EXACTLY the same as if the POI and POA were the same.

I've said right along that consistent cant has no deleterious effect on group size. But I need to work out for myself that distance between POA and POI has zero effect on group size assuming significantly inconsistent cant creeps in. Not saying you're wrong, in fact hoping you're right!
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[DShortt]

I am right there with you. I bought a scope mounted anti-cant device so that I can check to see the effects of cant myself. When I think about it if there is a considerable difference between POI and POA it seems plausible to me that any effects from cant would be multiplied but I'm not about to attempt to argue this position until I have tested it myself and know what I have observed for myself.
As you have said I actually hope the effect is the same because if not I've been chasing my tail and wasting time and ammunition for quite a long time.

 

[DShortt]

For your purposes and equipment, you're cutting it too fine. If you are shooting groups any larger that ~1/2" at 100 yds at this stage, I would allow at least 1.5 inches between POI and POA. Just avoid having POI, say, 3 or more inches away. Any effect of cant variability will be "down in the noise level" if you are a couple of inches from POA at that distance. For hunting, you will eventually adjust your scope for a reasonable point-blank range by setting POI 3" high at 100 yds (to pick a common rule of thumb figure).

Don't be too quick to dismiss your hunting equipment. I've developed loads for several OEM sporters w/ mid-level hunting scopes that consistently shoot 5/8" groups off a simple bipod or cheap front rest/bag off the bench. What is your ultimate goal for group size, with the gun and scope you are working with?

Edit: I suggest you take a common 8" plastic "torpedo" level with you to level your targets on the backer. Then adjust your bench setup so the the reticle aligns with the target for each shot.
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I'm in a bit of a bubble so to speak. I can pretty much shoot a 1" 5 shot group @100 yds off the bench on demand and occasionally manage a 3/4" group but I'm trying to get under that number but find I can't manage to. Given the equipment and techniques I've been using I think it's plausible that I've been handicapping myself a bit so I'm going to try a couple of different things as I mentioned. I understand the Indian behind the trigger is the most important part and I'm not saying otherwise at all.

 

[Brians356]

Given the equipment and techniques I've been using I think it's plausible that I've been handicapping myself a bit so I'm going to try a couple of different things as I mentioned. I understand the Indian behind the trigger is the most important part and I'm not saying otherwise at all.

To an extent it's the Indian, not the arrow. Unless you have a bent arrow. The inherent dispersion of your rifle and cartridge cannot be overcome with skill, only luck part of the time. It's always good to have a fellow shooter you know is much better than you shoot the rifle, and have him watch you shoot it.
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