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Old February 29, 2020, 01:39 PM   #26
Metal god
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Rear sight movement moves the bullet impact in the same direction, front sight movements are inverse
Yes I understand that . My question is if my sights are off the center bore axis because the front sight is canted off center to the left . As the distance I shoot gets longer , Does my POI shift from point of aim to the left or to the right .

Put another way , It's like your scope being above your bore . Your point of aim is straight through the scope which continues straight forever . this means you need to point your bore up so the bullet raises in flight to meet your scopes line of sight . In my case with the canted front sight , I need to move my rear sight over to line up with it . This puts mine straight line of sight to the left of my bore . Unlike a scope where the bullet comes up through my line of sight and then back down through it . With the sights off to the left of the bore , my bore needs to be pointed to the left the intersect with my off center sights line of sight .

Unlike the scope where the bullet just comes up to then back down through my line of sight . With my iron sights off to the left of my bore , I need to shoot my bullet not only up as we always do but to the left as well . The bullet is not coming back from the left , If I shoot it slightly to the left to intersect with my off axis sights the further the bullet travels the more left it will go correct ????

Which is what happened in that second group . All shots where 8"-ish off to the left at 300yds . Writing that all out answered my question haha .
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Old February 29, 2020, 03:20 PM   #27
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I think that the bullet(bore line) and sight line would cross at the point of intersection then the two would keep getting further apart.

Which direction... I can’t think about it too hard lol
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Old February 29, 2020, 03:50 PM   #28
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I doubt it will make a significant difference since you're talking about a tiny fraction of an inch of offset, at best.

Theoretically the point of impact will gradually move in the direction that the sight is offset from the bore but it will be a very small amount.

Let's say that the front sight cant results in the vertical plane of the front sight being offset from the vertical plane of the center of the boreline by 0.05" at the muzzle and you zero the gun at 100 yards.

That means the bore will be angled by the sight adjustment to remove the offset over the distance that the bullet travels to the target. So the bullet would move 0.05" towards the direction that the sight is offset over the 100 yards it travels to the target. You would expect that same amount of point of impact change for every 100 yards downrange past 100 yards.

So your offset at 1000 yards would be ((1000-100)/100)*0.05"=0.45"

But if you're shooting at 1000 yards, you probably wouldn't start with a 100 yard zero. So let's say you start with a 600 yard zero. Now you're moving the bullet toward the offset by 0.05" over 600 yards. Then you would expect another 0.05" of movement in the direction of the offset for every 600 yards downrange past 100 yards.

So your offset at 1000 yards with a 600 yard zero would be ((1000-600)/600)*0.05=0.033"

If you have a large sight offset and start with a relatively close zero, then you may see a detectable amount of point of impact offset when you shoot at ranges much longer than your zero. But with a small offset and a zero distance that is commensurate with the actual intended range, the result is going to be negligible.
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Old February 29, 2020, 04:56 PM   #29
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John those sound like solid numbers . Mine would be a tad different . I'm sighted in at 50yds and is there a multiplier because of the rear sight needing to line up with the front sight .

Or is it that my front sight is off .05 at the muzzle not at 50 or 100yds . I don't remember off hand but I think when I started with my mechanical zero my POI was off 3" from my POA at 50yds . However there is know way to know how perfectly my rear sight started over center ? Not sure if any of that changes the numbers ???
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Old February 29, 2020, 10:18 PM   #30
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The cant misaligns the sight in the vertical plane with respect to the line of the bore. That misalignment happens at (or near) the muzzle.

The ideal situation is that the sights and the boreline are perfectly (or at least very closely) aligned in the vertical plane. Then none of it matters. But if the front sight is canted so that there is a misalignment in the vertical plane then the rear sight will have to be adjusted to compensate. That will get the gun on target at the zero distance, but it will place the sights out of alignment with the boreline in the vertical plane.

The zero brings the bullet back to the point of aim at the zero distance. The bullet is being aimed so that the initial misalignment is compensated to zero at the range where the gun is zeroed.

But the bullet keeps traveling on that line after the zero distance. So if the sights are then adjusted for longer distances without rezeroing, (typically with elevation only adjustments) the vertical plane misalignment will grow from zero as the distance increases over the zero distance.

Ok, all of my analysis is based on the idea that we know the amount of front sight misalignment produced by the cant. If you don't know that, you can estimate it by looking at the difference in horizontal impact point at different zero distances.

So let's say you're zeroed at 50 yards and you see a horizontal impact error of 1" at 100 yards.

That suggests a 1" misalignment issue with the front sight. The bullet traveled 1" to the side in 50 yards (past the 50 yard zero) and that implies that it traveled 1" to the side in the 50 yards between the muzzle of the gun and the zero distance.

Obviously, that's a misalignment so large that it's unlikely, but that gives one a feel for what's going on.

Why is it an estimate? Because there are probably other things that can cause a horizontal error on the target besides sight misalignments.

The key, IMO, to not worrying about the sight cant issue is to zero at the longest practical range you can. This will minimize the amount of horizontal travel for the bullet over a given distance.
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I don't remember off hand but I think when I started with my mechanical zero my POI was off 3" from my POA at 50yds .
I'm inclined to think that this difference is related to something other than the sight cant. That would imply a sight to bore misalignment that is pretty much impossible.
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Old February 29, 2020, 11:12 PM   #31
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Small changes in your position for each group can cause those issues.
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Old March 1, 2020, 02:13 PM   #32
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Here is the target from the first 5 shot group , I marked the upper left ones so we can see them better .



The second 10 shot group did not have any shots on target . They were all slightly higher and a tad more left then those on the top left of target above .

Quote:
The key, IMO, to not worrying about the sight cant issue is to zero at the longest practical range you can. This will minimize the amount of horizontal travel for the bullet over a given distance.
I want the 50/200yd zero on this rifle . If I'm reading the above quote correctly . Instead of zeroing at 50 to also get a 200yd zero . I should zero at 200yds and see what I get at 50yds ? Interesting , That sounds like a good idea ??
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Old March 8, 2020, 03:02 PM   #33
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If I'm reading the above quote correctly . Instead of zeroing at 50 to also get a 200yd zero . I should zero at 200yds and see what I get at 50yds ? Interesting , That sounds like a good idea ??
Sorry for the delay responding.

From a horizontal sight displacement standpoint, yes, the 200yd zero should be best. By zeroing the gun at 200 yards, you're setting the bullet on a horizontal line that will eliminate the horizontal sight misalignment over a range of 200 yards. That's a much more gradual change than if you try to eliminate it all over a range over 50 yards.

That means that as the bullet continues on that line past the zero distance, it moves away from alignment at a rate 4x slower than it would with a 50yd zero (200/50=4).

But, again, the sight misalignment has to be pretty large and/or the range beyond the zero distance has to be pretty long before any of it makes a big difference.

As Bart says, there are other issues that are probably going to make bigger differences.
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Old March 8, 2020, 08:01 PM   #34
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Thanks John , I'm taking it back out tomorrow . I'll sight it in at 200 the see where it hits at 100 and 50 .
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Old March 9, 2020, 07:34 AM   #35
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You mentioned the wind was blowing when you had impacts to the left at 300 yds. Was the wind blowing right to left? And how fast was the wind? Doesn't take much wind to push things around at that distance. Take note of the wind today, if you get out to the range.
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Old March 9, 2020, 09:29 AM   #36
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Originally Posted by JohnKSa View Post
The cant misaligns the sight in the vertical plane with respect to the line of the bore.
Canting causes mostly horizontal shift in bullet's impact, very little vertically. Here's the formulas:

Sine of cant angle times bullet drop at target range equals horizontal shift in cant direction.

Cosine of cant angle times bullet drop at target range equals down vertical shift.
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Old March 9, 2020, 06:54 PM   #37
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You mentioned the wind was blowing when you had impacts to the left at 300 yds. Was the wind blowing right to left? And how fast was the wind? Doesn't take much wind to push things around at that distance. Take note of the wind today, if you get out to the range.
Wind that day was 5 to 10mph from 4 to 10 o-clock so yes it was blowing right to left a bit .

Today it was calm-ish , nothing really worth noting or that I remember .

Today I zeroed at 200 which resulted in a 1" to the right impact from POA at 50yds . I was not happy but after doing some rapid off hand shooting at 50yds It was clear that 1" to the right was not noticeable . My 20 shot group at 50yds was 8 to 10 inches in size with it being relatively consistently dispersed around POA .

Am I happy , No . Can I live with it , I think so but time will tell . If I know me , I'll likely pull the front sight base at some point and see If I can straighten it out but for now I'm OK-ish with it .
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Old March 9, 2020, 09:02 PM   #38
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. Wind that day was 5 to 10mph from 4 to 10 o-clock so yes it was blowing right to left a bit .
With a 55 gr boat tail that would account for a big portion of the left of POA. And it sounds like with no wind it was right of POA at 200. Doesn't sound like the rear sight position is so much of an issue. But I get how it bugs you, I would bother me too. I had a muzzleloader like that.....drove me nuts.
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Old March 10, 2020, 01:25 AM   #39
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Canting causes mostly horizontal shift in bullet's impact, very little vertically. Here's the formulas:

Sine of cant angle times bullet drop at target range equals horizontal shift in cant direction.

Cosine of cant angle times bullet drop at target range equals down vertical shift.
Yes, everything you say is true.

I was quite sloppy in the particular statement you quoted although I was more clear elsewhere. The comment you quoted was a not so precise rephrase of an earlier comment I made about the cant misaligning the vertical plane of the front sight with the vertical plane of the boreline.

Also, as you say, there is a vertical displacement as well due to the cant. I ignored that because, as you say, it is small for cants likely to be encountered (small ones), and because the OP seemed focused on the horizontal effect on the POI.

I should have been more thorough in my explanation.
Quote:
Today I zeroed at 200 which resulted in a 1" to the right impact from POA at 50yds
That's really too much POA/POI difference at 50 yards to be accounted for by a canted front sight.

Let's take the extreme worse case scenario where the sight is canted a full 90 degrees so it's pointing directly out the side of the barrel--level with the ground. Now let's say the gun is zeroed at 200 yards and when you shoot it at 50 yards, the POA is off to one side by an inch.

For the POA/POI difference to be off at 50 yards by 1 inch with a 200yd zero, the "top" of the front sight would have to be about 1.33" from the boreline. That might make sense with an extreme cant like the one in this unrealistic example, but for smaller values, it's hard to see how you could get enough cant to get that much horizontal displacement at 50 yards with a 200 yard zero.

I think there's something else going on.

Anyway, at least it's workable with the 200yd zero.
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Old March 10, 2020, 02:33 AM   #40
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For the POA/POI difference to be off at 50 yards by 1 inch with a 200yd zero, the "top" of the front sight would have to be about 1.33" from the boreline.
No it wouldn't , Are you taking into account the other focal point ? There's a rear sight as well ??. Every inch the rear sight is moved forward or rearward will move the ass end of the rifle more or less depending on placement of the rear sight . Shouldn't you need the exact distance between the sights to make an accurate assessment ? as well as how far forward my muzzle is from the front sight ?

Kind like a short or long wheel based car . It's why longer sight radius is easier to shoot accurately . The shorter the sight radius the squallier the gun gets .

If my front sight was canted 1.5" to the left off the center bore line . Wouldn't my rear sight need to be at least 2" left of the bore line for the sight line and bullet path to intersect around 50yards .

I thought BartB wrote once the muzzle only needs to be off a fraction of an inch to throw your bullet off by inches down range .

I mean I'm not yanking my muzzle over an inch with trigger flinch on each shot . I might not be a great shot but I shoot pretty good if you ask me . Go ahead ask , I'll tell ya
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Old March 10, 2020, 06:35 PM   #41
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I have another example

I sighted in a new scope the other day and my first shot was about 4" to the right at 50yds . The scope has a 1" tube . I promise you I did not need to move the reticle 1.5" to get on target at 50yds
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Old March 10, 2020, 06:47 PM   #42
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I still think it wouldn’t be that big of a deal to simply correct the misalignment. Even if it took a trip to a gunsmith, I’m sure a decent one could make quick work of it.
However, me being me, I’d attempt it myself.
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Old March 11, 2020, 12:33 AM   #43
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If my front sight was canted 1.5" to the left off the center bore line . Wouldn't my rear sight need to be at least 2" left of the bore line for the sight line and bullet path to intersect around 50yards .
At the zero distance, the bullet path (which starts from the bore) will intersect the sight line which by definition goes through the front sight.

If the front sight is 1.5" off to the side of the bore, then you are correcting that 1.5" error with the rear sight (if possible) so that the sight line and bullet path intersect at the zero distance.

Draw imaginary lines from the bore and from the front sight to the zero distance where they meet. The lines will be 1.5" apart at the bore (if your front sight is canted 1.5" to the side) and will intersect at the zero distance. In between, as you move closer to the zero distance, they will get closer and closer together.

Getting back to your situation but keeping the imaginary lines in mind, if you are seeing a 1" error at 50 yards with a 200 yard zero, the front sight must be off more than that at the muzzle if cant is the only issue. If you work out the trig, it comes out to about 1.33" at the muzzle. Since your front sight cant is not moving it out of alignment with the muzzle by 1.33", the error you are seeing can't be accounted for by the sight cant. It may be part of the problem but there's something else going on.
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I thought BartB wrote once the muzzle only needs to be off a fraction of an inch to throw your bullet off by inches down range .
That is certainly true. However, we're talking about the case where we've already adjusted the sightline and boreline to intersect at the zero distance and discussing what happens to that line before and beyond the zero distance.
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I sighted in a new scope the other day and my first shot was about 4" to the right at 50yds . The scope has a 1" tube . I promise you I did not need to move the reticle 1.5" to get on target at 50yds
Very different than having one component of an iron sight system off by 1.5" and having to compensate with the other one and the resulting geometry. Thinking about scopes will not help with this problem--it will only confuse the issue. They work very differently than iron sights--at least for the purposes of this discussion. If you want to think about it from a scope perspective, the roughly equivalent scope situation would be with the scope body mounted so that it is offset horizontally from the bore by a significant amount. That's still not the same, but it's sort of in the ballpark.
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Old March 11, 2020, 03:58 PM   #44
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This all makes my head hurt. If the rear sight is moved to correct the front sight cant, the rifle will have to be held canted while shooting, in order to not have the compounding error beyond the zero range.

And to make things worse it's also not unheard of to have some rifle barrels who's bores are not drilled/hammered concentrically in the barrel.
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Old March 12, 2020, 09:21 PM   #45
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Funny thing, I was going over some of my weapons today and one of my ARs has a diamond head branded sight on the rear that is real similar to the sight that you have... different brands of course.
I noticed that the aperture is left of center just like yours. This AR has the standard AR sight post. Don’t think that it is canted, I think it’s just where it’s zeroed.
This AR was scoped in the past, but I switched it back to iron sights because I figured I wouldn’t use this one for long ranges.
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