Point of aim vs point of impact

[DShortt]

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.

 

[divingin]

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.

Huh? If you're set up for an offset but not tracking the difference between POA and POI, are you even aiming? Sure, use a separate aim point, but that offset should be consistent shot to shot for a given distance, which implies you have to pay attention to the difference (assuming you're trying to hit something, anyway.)

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?

Makes sense, but I think it's somewhat misleading. Error from cant will get worse as you change distance (for a particular orientation); it will remain the same at a single distance (for a particular orientation.)

All rifle configurations will suffer from some degree of cant effect as the sight is mounted above the barrel. A coincidental POA/POI assumes a vertically plumb centerline of both bore and scope. Offset the centerlines and you change the intersection of sight and shot. So I'm not sure you can say that changing the offset increases potential error. It's always there regardless.

Now add in ballistics - you're not shooting a laser beam. Your bullet (assuming POA/POI congruence) has to rise from the sightline/bore offset to the POA (for close distances.) Continuing downrange, it rises more, then drops back down to POA again, then drops further. For longer range solutions, you are shooting the second POA/POI congruence (i.e. lobbing the bullet through the sightline, and allowing it to drop back in to the target.) Cant launches the bullet horizontally divergent to the sight line, which induces a horizontal error on target. By using a coincidental POA/POI, you minimize that effect, but you don't eliminate it.

Note that all the above drivel is theoretical. I don't really pay all that much attention to it while shooting.

TLDR Bottom line: It's complicated.

 

[jelenko]

Group size should not be affected by having POI different than POA. Variations in amount of cant will have he same effect. Assuming the POI and POA are at the same distance.

 

[DShortt]

Huh? If you're set up for an offset but not tracking the difference between POA and POI, are you even aiming? Sure, use a separate aim point, but that offset should be consistent shot to shot for a given distance, which implies you have to pay attention to the difference (assuming you're trying to hit something, anyway.)

I'm sorry, I didn't word that very well. What I meant was up to now I've just made enough scope adjustment during initial sighting to get within an inch or 2 of my point of aim. After that when I've changed loads I never worried about how far from the point of aim the center of the group was. As long as it was on a 8 1/2" x 11" sheet of copy paper then I didn't worry about it. I just put a Birchwood - Casey 1" orange target dot close to center on a sheet of copy paper and that's what I use for range targets. I don't hunt with any of these guns/loads so I never worried about that POA and POI matching and often they'll be different by 3" or more both vertical and horizontal. Hopefully that explains what I've been doing more. Might explain where I've been screwing up too?

 

[CharlieNC]

Based on your description of issues, study more about natural point of aim.

 

[divingin]

As long as it was on a 8 1/2" x 11" sheet of copy paper then I didn't worry about it. I just put a Birchwood - Casey 1" orange target dot close to center on a sheet of copy paper and that's what I use for range targets. I don't hunt with any of these guns/loads so I never worried about that POA and POI matching and often they'll be different by 3" or more both vertical and horizontal. Hopefully that explains what I've been doing more. Might explain where I've been screwing up too?

"Screwing up" implies you have a goal.

For group shooting, you want all shots to end up in the same place; doesn't matter much where. For score, you're going for a particular spot on the target. For steel, you're trying to hit an area. And then there's guys who just want to make noise, and don't care what they hit (I hate those guys...)

Changing loads will change POI; that's kind of a given. Or maybe I'm unclear on what your issue is.

That said, if you look at the standard benchrest target, it has a square that many use for offset sighting. I use practice targets for day to day shooting; those have the center portion of the standard target repeated a bunch of times. For boresighting, I put a dot to the side of the target paper and take a shot at that, then move the scope to the shot. No right way to do things, IMO.

 

[22BRGUY]

You might want to check your bullet trajectory (arc) for the particular bullet, weight,
design and velocity you are using also for various distances.

 

[jelenko]

I'm sorry, I didn't word that very well. What I meant was up to now I've just made enough scope adjustment during initial sighting to get within an inch or 2 of my point of aim. After that when I've changed loads I never worried about how far from the point of aim the center of the group was. As long as it was on a 8 1/2" x 11" sheet of copy paper then I didn't worry about it. I just put a Birchwood - Casey 1" orange target dot close to center on a sheet of copy paper and that's what I use for range targets. I don't hunt with any of these guns/loads so I never worried about that POA and POI matching and often they'll be different by 3" or more both vertical and horizontal. Hopefully that explains what I've been doing more. Might explain where I've been screwing up too?

I do this type of the thing a lot when I testing loads. Because I test from prone with a sling, my POA is the center X ring. I move the POI for each group around the target. For example, I'll have one load tested at 2 MOA above the x ring, another 2 MOA to the right, etc.

What you're doing is just fine - assuming you're using the same load for each POI.

 

[DShortt]

I do this type of the thing a lot when I testing loads. Because I test from prone with a sling, my POA is the center X ring. I move the POI for each group around the target. For example, I'll have one load tested at 2 MOA above the x ring, another 2 MOA to the right, etc.

What you're doing is just fine - assuming you're using the same load for each POI.

Ok, sounds like we're basically doing the same thing the only difference being you are making scope adjustments to change your POI while my POI changes are happenstance due to load/bullet changes. However we are both utilizing a set POA. Thanks.

 

[JMayo]

Bench rest competition rifles
Here is a target i shot. Poa is the 90° of the orange square bottom left "L" every row is different powder charge + .2
I look for change in vertical with the groups. Hot barrel plays a role.

I also have a ar with an eotec holographic.
To cant it left makes the holographic go way right. Seeing this taught me how important level is.
It Also answered the problem i had at 600yds, my bullets always went high and right on top target but just right by half on bottom target.
IBS 600 yds targets.
If you have a red dot on any guns try this out and see for yourself.

 

[DShortt]

View attachment 1371565
Bench rest competition rifles
Here is a target i shot. Poa is the 90° of the orange square bottom left "L" every row is different powder charge + .2
I look for change in vertical with the groups. Hot barrel plays a role.

I also have a ar with an eotec holographic.
To cant it left makes the holographic go way right. Seeing this taught me how important level is.
It Also answered the problem i had at 600yds, my bullets always went high and right on top target but just right by half on bottom target.
IBS 600 yds targets.
If you have a red dot on any guns try this out and see for yourself.

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.

 

[Rtheurer]

I see this every day at the range ( I work at one) Guys will come to the range and do LOAD Development or TEST Different Boxes of factory ammo in their gun. They will set there POI at the same POA. Tearing a big dam hole in the target and after a few rounds have NOTHING to actually aim at. If you click high,LOW, Left, or Right from POA you have something to actually aim at.
SO in my eyes, I see the original poster doing it correctly. Once the descision of what is working best is made... then you can go ahead and set your scope for the Zero distance that you want on your rifle.

 

[DShortt]

Well this is where I'm confused. I completely understand not blowing a big hole in the target and completely destroying the POA. What I'm not clear on if it's perhaps detrimental to group size to leave the POA and POI apart by several inches. This isn't wind drift or the effects of light or any other variable. I'm not intimately familiar with ballistics so this might be off some but if you're 3" high and 3" right @100 then it seems things like cant *might* make considerably more difference than it would if you were 1" high and 1" right. I'll have to check this at the range before I would attempt to argue that point, this is simply something that seems plausible to me and perhaps I'm completely mistaken.
I hope I'm explaining my thoughts correctly. It's difficult to make words match ideas sometimes.

 

[JMayo]

Indoor 100 yrd. It does have drafts from fan openings. Fans were off.
Those are 1" squares. My poi is .5 up and .5 right. Normally i want group in center of square. I might have adjusted durring group test to achieve that. As the charge went up the poi changed.
Again barrel heat also plays a role.

I've also seen in an indoor with sky lights, if clouds cover sun shine poi is affected. So if it's a partly cloudy sun bird day and a big cloud comes don't shoot until it clears or only shoot that group while sun is covered.

 

[Sandstorm]

Aim small shoot small...your 1 inch dot is much too big for a point of aim in my book.
YMMV and it will.

 

[DShortt]

Aim small shoot small...your 1 inch dot is much too big for a point of aim in my book.
YMMV and it will.

That's also a good point. The scopes I'm using are not target scopes so it's difficult at best to see well. I'd not been worried about upgrading until I got to the point where I felt it would make a difference and it seems that time is here or very near.

 

[Coyotefurharvester]

Canting is an angular issue, so distant is more of a factor than having a poa/poi offset. Have the aiming point, large enough so you can center the reticle the same shot to shot. You need to be able to call your shot.

 

[Sandstorm]

I use a dot the size of my bullet...284....and thats too big. you really need an X
and aim for the bottom of the V in the X
( Dial up 1 MOA so you don't destroy your point of aim of course. )

 

[Brians356]

aim for the bottom of the V in the X

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.)
-

 

[redrockranger]

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.

Do you site scope using a good rest ?