Vertical alignment of Rifle and Scope?

[CNP]

Tell me you do not understand this...

[Pathfinder76]

Originally Posted by CNP

Tell me you do not understand this...

Again, the scope MUST be level. The rifle no.

[catnthehat]

Originally Posted by Off in the Bushes

But isn't that the point of discussion is that the POI changes with the same zero as the rifle or scope becomes canted.

You all are beginning to lose me in this discussion now.

One side is stating that both scope and rifle have to both be level.
The other sude is saying if the scope is level it it doesn’t Matter if it is level on a canted rifle if the scope is consistently level
Cat

[Off in the Bushes]

Originally Posted by catnthehat

One side is stating that both scope and rifle have to both be level.
The other sude is saying if the scope is level it it doesn’t Matter if it is level on a canted rifle if the scope is consistently level
Cat

So the big debate is between the left and right image?

[Salavee]

Originally Posted by catnthehat

A fourth diagram is needed with a canted rifle and level crosshairs - crosshairs that are consistently level with the use of a level .
Cat

I hear where Chuck is coming from. Due to being a lefty shooting a lot if right handed rifles, cant is usually an issue for me..
When mounting scopes, once everything is lined up true to the bore I then use my grid style bore sighter to adjust the cross hairs to the grid with the rifle mounted as I would shoot it. Any right handed shooter always thinks my cross hairs aren't verticle, but they are for me. I Never have an issue with cant.

[elkhunter11]

Originally Posted by Big Lou

Guys, Andrew and Chuck are dead nuts correct here. I’ll be the first to admit that I struggled with getting my head around this concept and eventually ended up having to prove it for myself. Tall target tests showed the proof in the pudding.

I think the way I would try and explain this to someone would be to use grid paper for simplicities sake. Draw yourself a reticle. Standard duplex, hold over - whatever your flavour is. This represents your leveled scope and reticle. Pick an arbitrary mark below your reticle and off to the side. This would represent a canted rifle bore. Not to be confused with a canted reticle. Assume the rifle and scope are zeroed to one another. Your canted rifle will be a constant as well as your levelled reticle. Now draw a vertical line coming from the center of your reticle up, representing a hold over whether dialled or using the reticle. Draw a vertical line straight up from your arbitrary mark representing the center of your bore. It will be exactly the same distance center of reticle to center of bore as far up as you care to carry it. Regardless of rifle cant, if your reticle remains level then your cant will also be constant and will follow one another respectively.

Like I said, I’m the first to admit I struggled with it too.

It is true that the horizontal distance between those two lines you mention will be the same no matter how long they are. For that reason the scope will track properly at all distances. As long as you are willing to accept that the horizontal distance between the crosshairs and point of impact will be the same as the distance between those two lines that you just drew, you can have that same distance at all ranges you shoot. But there is no way to adjust the scope to make the horizontal distance between those lines disappear at all ranges. If you don't understand that, draw two parallel lines, one representing the bore and the other representing the center of the crosshairs, as viewed from the top of the rifle. Now rotate the line representing the center of the crosshairs until it intersects the line representing the center of the bore. Notice that the two lines can only intersect at one point, which means that you can only eliminate the difference between those two lines at one range. If you could move the entire scope straight sideways the distance between those two lines, this wouldn't be an issue, but when you move the scope adjustments, you don't move the entire scope sideways, you twist the erector at an angle to align the crosshairs with the bore.

[CNP]

Originally Posted by chuck

Again, the scope MUST be level. The rifle no.

It doesn't matter. A canted rifle with a level crosshair is the same as a scope that is not level. Exactly the same. Rotate the second drawing until the crosshair is level and you have a canted rifle. All vertical reference points MUST be pointed down the barrel, if the rifle is canted and the scope is level.....guess what...….. it is impossible for all vertical reference points to be pointed down the barrel. Impossible.

[catnthehat]

Originally Posted by Off in the Bushes

So the big debate is between the left and right image?

I think one school of thought is that figure one is the only way to shoot accurately , the other school of thought is that if figure three is totally acceptable as well .
Either will work as long as the sighting devices is consistently level.
Cat

[CNP]

Originally Posted by elkhunter11

It is true that the horizontal distance between those two lines you mention will be the same no matter how long they are. For that reason the scope will track properly at all distances. As long as you are willing to accept that the horizontal distance between the crosshairs and point of impact will be the same as the distance between those two lines that you just drew, you can have that same distance at all ranges you shoot. But there is no way to adjust the scope to make the horizontal distance between those lines disappear at all ranges. If you don't understand that, draw two parallel lines, one representing the bore and the other representing the center of the crosshairs, as viewed from the top of the rifle. Now rotate the line representing the center of the crosshairs until it intersects the line representing the center of the bore. Notice that the two lines can only intersect at one point, which means that you can only eliminate the difference between those two lines at one range.

Yes

[Pathfinder76]

Originally Posted by CNP

Yes

Rotate your picture until the crosshairs in picture number 2 are level. Your crosshairs must be level. Your bullet does not follow the rifles alignment it reacts to gravity.

[CNP]

Originally Posted by catnthehat

I think one school of thought is that figure one is the only way to shoot accurately , the other school of thought is that if figure three is totally acceptable as well .
Either will work as long as the sighting devices is consistently level.
Cat

Image two and three are to be treated as the same. Image three is just image two rotated...….look at it in your mind...... rotate image two until it looks like image three. The canted explanation is no more than a scope that is not mounted on a level rifle. Image one has a scope mounted correctly.

[elkhunter11]

Originally Posted by chuck

Rotate your picture until the crosshairs in picture number 2 are level. Your crosshairs must be level. Your bullet does not follow the rifles alignment it reacts to gravity.

Rotate the entire piece of paper until the crosshairs are level in the right diagram. Then drop one line down through the center of the crosshairs, and one line down through the center of the bore. The distance between those lines is the horizontal offset. you can't eliminate that offset at all distances with the windage adjustment.

[CNP]

Originally Posted by chuck

Rotate your picture until the crosshairs in picture number 2 are level. Your crosshairs must be level. Your bullet does not follow the rifles alignment it reacts to gravity.

We aren't talking about gravity. We are talking about horizontal error, not vertical error. See the horizontal error between 200 and 600 yards. You are turning the rifle and scope as one unit, doing so does not change the horizontal error, it retains it.

[Salavee]

Originally Posted by chuck

Again, the scope MUST be level. The rifle no.

I'm with Chuck on this one. Introduce some cant until the cross hair is verticle and you're good to go.


Wrong ... Not quite what i meant.

[marky_mark]

You need to add a rifle stock to you picture to relate cant of the rifle

If stock bore and scope are level
No problem
If stock bore canted scope level
Theoretically the same ( I don’t think it will be perfect. Could be wrong)
If stock bore is level scope is canted
Problems

1 is simplist and easiest

Throw in a 20moa base and only 1 works

[elkhunter11]

Originally Posted by CNP

We aren't talking about gravity. We are talking about horizontal error, not vertical error. See the horizontal error between 200 and 600 yards. You are turning the rifle and scope as one unit, doing so does not change the horizontal error, it retains it.

If the scope and bore are perfectly parallel, the horizontal offset can actually be the same at all ranges. But no matter how you adjust the scope, you can't eliminate that error at more than one range.

I'm with Chuck on this one. Introduce some cant until the cross hair is verticle and you're good to go.

If you do as Chuck suggested, and rotate drawing 2 until the crosshairs are level, the bore moves off to the side, creating horizontal offset.

[Scottmisfits]

The first diagram is the proper way. That being said, one of the first things we will.hear about guys shooting at these ridiculous long ranges is that it's unethical hunting and most shots are taken within 200 yards.

From what I gathered in one of Chuck's earlier posts is that inside normal.huntjng distances, crosshairs level with your hold is good. The horizontal difference wod be negligible. It's there but Bary noticable for hunting purposes.

Target and precision shooting, level, square, plumbing, etc, get them lined up properly for shooting past , what, maybe 400 yards? That's when it will really start to become a little more noticeable maybe.

All that being said, this effect would really be amplified if the centerline of the scope or and bore aren't perpendicular to each other. Throw in a MOA Ra and the effects amplify greatly.

[elkhunter11]

Originally Posted by Scottmisfits

The first diagram is the proper way. That being said, one of the first things we will.hear about guys shooting at these ridiculous long ranges is that it's unethical hunting and most shots are taken within 200 yards.

From what I gathered in one of Chuck's earlier posts is that inside normal.huntjng distances, crosshairs level with your hold is good. The horizontal difference wod be negligible. It's there but Bary noticable for hunting purposes.

Target and precision shooting, level, square, plumbing, etc, get them lined up properly for shooting past , what, maybe 400 yards? That's when it will really start to become a little more noticeable maybe.

All that being said, this effect would really be amplified if the centerline of the scope or and bore aren't perpendicular to each other. Throw in a MOA Ra and the effects amplify greatly.

With a few degrees of cant, the difference would be negligible for big game hunting at the distances that most people shoot at. As the cant increases, or the scope mounting height increases, so does the horizontal offset. So if you use a 50mm scope mounted high on a varmint rifle, and you cant the rifle, it could cause more misses trying to shoot the heads off of ground squirrels at 200-300 yards. For the person shooting targets at 1000 yards, it would definitely be something to consider. But regardless of the situation , if you cant the rifle, you will have horizontal offset, whether you realize it or not.

[Scottmisfits]

Agreed. I think we really said the same thing, just in a different way.

[AndrewM]

Originally Posted by CNP

Tell me you do not understand this...

This isn’t even a correct picture. Twist side ways for level cross hairs. Center your scope. Vertical adjustment is the same for all. You end up with picture one once you rezero! Nobody is saying crooked crosshairs won’t affect vertical movement!

[DiabeticKripple]

If you mount the scope level, on a slightly canted rifle, you are moving the Center of the scope crosshairs to the side.

You are now inducing an angle to the target which will have to be compensated at different ranges for windage.

Can’t argue with physics.

[Salavee]

Originally Posted by elkhunter11

With a few degrees of cant, the difference would be negligible for big game hunting at the distances that most people shoot at. As the cant increases, or the scope mounting height increases, so does the horizontal offset. So if you use a 50mm scope mounted high on a varmint rifle, and you cant the rifle, it could cause more misses trying to shoot the heads off of ground squirrels at 200-300 yards. For the person shooting targets at 1000 yards, it would definitely be something to consider. But regardless of the situation , if you cant the rifle, you will have horizontal offset, whether you realize it or not.

WoW.this is getting interesting. I was chiding Chuck a Bit on that post. My take is my post 95. I think it's important to level the 'scope using the same hold as you would be shooting it to counter any shooter induced cant .

That way, the scope itself is still aligned with the bore and the scope is level while shooting any small errors in verticle and horizontal can be corrected at the range.
. I think this confusion comes from setting up the 'scope in a vise rather than by shooter hold, with the individuals cant included. Could be wrong but it seems to work. I really think Chuck was eluding to the same procedure, but you never know with him. I'll take a properly fitted stock any day.

[Nyksta]

If the crosshair is always held level to gravity, then the shooters aim will be consistent. If the rifle bore is offset to a side instead of directly underneath, then when zeroing the shot, the shooter must zero with the impact slightly to whatever side the barrel is offset from underneath the scope. On a center mounted rifle that the scope is not perfectly level overtop the bore, when shooting the scope must be level, then realistically, the impact might be out a very small amount, and not really an issue if its for hunting big game. A centimeter right at muzzle, a centimeter right at 100 and a centimeter right at 500…. As long as the scope is level to gravity, the bullet will rise and fall parallel to the vertical line in the crosshair. Is a small offset really worth worrying about? If you have the option to get a proper "over the bore" alignment, then remount your scope properly and be done with the offset shots. Check out the Bren Gun offset sights... Or wwi smle sights. Many systems didnt have "over the bore" aiming, and it still works.

[CNP]

Originally Posted by AndrewM

This isn’t even a correct picture. Twist side ways for level cross hairs. Center your scope. Vertical adjustment is the same for all. You end up with picture one once you rezero! Nobody is saying crooked crosshairs won’t affect vertical movement!

You have no idea what is going on here. The picture is correct. HORIZONTAL offset is what this is about.

[mattthegorby]

Originally Posted by elkhunter11

It is true that the horizontal distance between those two lines you mention will be the same no matter how long they are. For that reason the scope will track properly at all distances. As long as you are willing to accept that the horizontal distance between the crosshairs and point of impact will be the same as the distance between those two lines that you just drew, you can have that same distance at all ranges you shoot. But there is no way to adjust the scope to make the horizontal distance between those lines disappear at all ranges. If you don't understand that, draw two parallel lines, one representing the bore and the other representing the center of the crosshairs, as viewed from the top of the rifle. Now rotate the line representing the center of the crosshairs until it intersects the line representing the center of the bore. Notice that the two lines can only intersect at one point, which means that you can only eliminate the difference between those two lines at one range. If you could move the entire scope straight sideways the distance between those two lines, this wouldn't be an issue, but when you move the scope adjustments, you don't move the entire scope sideways, you twist the erector at an angle to align the crosshairs with the bore.

For me this is all academic and will not impact my shooting, but I gotta say this is the only description of the physics that I can get my head around.

[AndrewM]

Originally Posted by CNP

You have no idea what is going on here. The picture is correct. HORIZONTAL offset is what this is about.

Then replace what I said and state horizontal. If you zero the scope with the rifle after leveling the crosshairs you get picture 1! I will draw you a picture when I get to work. If you can’t your rifle from picture 1 to 2 then of course you have a different point of impact. But as soon as you rezero you have picture 1 again.

[elkhunter11]

Originally Posted by AndrewM

This isn’t even a correct picture. Twist side ways for level cross hairs. Center your scope. Vertical adjustment is the same for all. You end up with picture one once you rezero! Nobody is saying crooked crosshairs won’t affect vertical movement!

The picture is not correct, but rotating the picture will not make picture 2 into picture one. The bore and crosshairs will still be offset horizontally, and it's not as simple as adjusting the scope, because a scope adjusts windage by changing angles, not by moving the entire scope sideways. That is why scope specifications list angular correction , as in minutes, rather than mm or parts of an inch. If you could pivot your scope mount back over the bore, that would eliminate the offset, but most scope mounts don't allow for that.

[AndrewM]

Originally Posted by elkhunter11

The picture is not correct, but rotating the picture will not make picture 2 into picture one. The bore and crosshairs will still be offset horizontally, and it's not as simple as adjusting the scope, because a scope adjusts windage by changing angles, not by moving the entire scope sideways. That is why scope specifications list angular correction , as in minutes, rather than mm or parts of an inch. If you could pivot your scope mount back over the bore, that would eliminate the offset, but most scope mounts don't allow for that.

I get what you are saying. Do you center your scope for windage optically then and shim to adjust to target?

[Pathfinder76]

Well lookie here. Huh.

https://youtu.be/eCoHG23TQcY

[elkhunter11]

Originally Posted by AndrewM

I get what you are saying. Do you center your scope for windage optically then and shim to adjust to target?

No I don't. But I don't purposely introduce offset by canting my rifles either. If I found that I needed to cant my rifles for them to fit my shoulder properly, I would install an adjustable butt plate instead, just as many shotgun clays shooters do. Whether of not the shooter can detect the offset, I prefer to not purposely introduce any.