Size of target at 800 yards? And how close to center?

el matador

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A couple of thoughts -

It's not possible for a flexible rope to hang diagonally unless there is some lateral force being exerted on it (such as wind). Any torque that is generated by the block being off center will simply bend the rope at the point of least resistance (right next to the block), and the rope will end up being plumb.

Canting the scope to compensate for spin drift isn't a bad idea. Spin drift and scope cant both have a parabolic effect on POI and the curves are pretty similar, although they do start to diverge after 1500 yards or so. You'd need somewhere around 2 degrees of clockwise cant on the scope. For simplicity it would probably be best to mount the scope straight, in line with the bore centerline, and then rotate your scope level 2° clockwise. You could use the posterboard technique to get the scope mounted square to the gun and then draw a 2° line (or whatever angle you figure) to make the adjustment to your level.
 

WildRose

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This might be a stupid question but I have seen this on one of the long range hunting shows..they put a cant in the scope to take out spin drift. With now when my action is level as pics showed my crosshairs off center counter clockwise a bit (so there moving down and right when dialing long range) With my cross hairs off counter clockwise I offset that by rotating clockwise to level on my scope. This in turn rotates my level bore to cant clockwise ( when I shoot with that set up my hits are left of target, does that seem right with impacts??

Because what I'm wondering for the time being level my action ( scope is cant counter clockwise) move my level on my scope to match my bore..so spin drift is to the right but scope is offsetting that with it mounted counter clockwise and moving up and left, then maybe the bullet meets in the middle??

Thought it was worth asking since I'm sure I saw it once, then during offseason get things squared up.
There simply is no way to accurately cant your scope purposely to take out spin drift with any accuracy at all.

Whomever is suggesting attempting to do so is trying to sell you a wagon load of BS.

That is why we have ballistic calculator apps for just about every electronic device on the market today. You would be better off simply guessing at spin drift and holding a little more left than attempting to eliminate it by canting the scope.
 

MontanaRifleman

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A couple of thoughts -

It's not possible for a flexible rope to hang diagonally unless there is some lateral force being exerted on it (such as wind). Any torque that is generated by the block being off center will simply bend the rope at the point of least resistance (right next to the block), and the rope will end up being plumb.

After thinking about it, this is right. The block will center it's gravity on the rope so the problem is not induced by a canted rope.

I agree that canting the scope to account for spin drift is not a good idea.
 

el matador

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There simply is no way to accurately cant your scope purposely to take out spin drift with any accuracy at all.

Can you expound upon this a little? Also wondering if it's your opinion or if you can cite some facts or data to illustrate why it can't be done "with any accuracy at all". I am only looking at charts and equations, and I think it looks like a very viable solution. Many shooters will sight in a little bit left to offset the effects of spin drift out to 700 yards or so, and that's using a straight line of sight to offset a parabolic curve. Clearly those paths would diverge sooner than if you matched one parabolic curve to another. I'm not trying to be argumentative, just saying that the data I see makes it look like a good idea. I want to learn as much as I can from everyone here and I would welcome any experiences or calculations that refute the data I've come up with. I'm attaching some numbers from the ballistics calc.

Now I realize that spin drift will vary slightly with changes in air density, but out to 1200 yards those changes only amount to a couple of inches.
 

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MontanaRifleman

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Can you expound upon this a little? Also wondering if it's your opinion or if you can cite some facts or data to illustrate why it can't be done "with any accuracy at all". I am only looking at charts and equations, and I think it looks like a very viable solution. Many shooters will sight in a little bit left to offset the effects of spin drift out to 700 yards or so, and that's using a straight line of sight to offset a parabolic curve. Clearly those paths would diverge sooner than if you matched one parabolic curve to another. I'm not trying to be argumentative, just saying that the data I see makes it look like a good idea. I want to learn as much as I can from everyone here and I would welcome any experiences or calculations that refute the data I've come up with. I'm attaching some numbers from the ballistics calc.

Now I realize that spin drift will vary slightly with changes in air density, but out to 1200 yards those changes only amount to a couple of inches.

Impact deviation due to cant is dependent upon where you zero If you zero @ 100 the impact deviation @ 1000 will be greater than if you zero @ 200 or 300.

If you zero @ 200 there will be no impact deviation @ 200 because you are zeroed there. POI and POA are the same. Deviation will begin after the zero point. I believe it would be impossible to align the spin drift and cant curves.

Also, there are different types of cant errors such as cant with bore and wingage reticle aligned and cant when bore and windage reticle is not aligned.
 

WildRose

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Can you expound upon this a little? Also wondering if it's your opinion or if you can cite some facts or data to illustrate why it can't be done "with any accuracy at all". I am only looking at charts and equations, and I think it looks like a very viable solution. Many shooters will sight in a little bit left to offset the effects of spin drift out to 700 yards or so, and that's using a straight line of sight to offset a parabolic curve. Clearly those paths would diverge sooner than if you matched one parabolic curve to another. I'm not trying to be argumentative, just saying that the data I see makes it look like a good idea. I want to learn as much as I can from everyone here and I would welcome any experiences or calculations that refute the data I've come up with. I'm attaching some numbers from the ballistics calc.

Now I realize that spin drift will vary slightly with changes in air density, but out to 1200 yards those changes only amount to a couple of inches.
Without your scope tube and rings being calibrated and marked you are just guessing and approximating the cant.
 

el matador

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Impact deviation due to cant is dependent upon where you zero If you zero @ 100 the impact deviation @ 1000 will be greater than if you zero @ 200 or 300.

If you zero @ 200 there will be no impact deviation @ 200 because you are zeroed there. POI and POA are the same. Deviation will begin after the zero point. I believe it would be impossible to align the spin drift and cant curves.

Also, there are different types of cant errors such as cant with bore and wingage reticle aligned and cant when bore and windage reticle is not aligned.
I disagree with you on the zero range impacting cant error. Imagine using a lazer bore sighter at 1000 yards to show you where the barrel is aimed. That lazer will be 10-15 feet above your point of aim once you dial elevation for 1000 yards. Now cant your scope left and right and watch the lazer move horizontally with respect to your point of aim. Cant error is a function of the misalignment of bore axis and line of sight. As a test, take a gun that's zeroed at 200 yards and shoot it canted 90° clockwise. I guarantee you won't hit the bullseye. Rather you will hit several inches to the right.

I'll have to think about the windage + cant scenario for a bit :D
 

WildRose

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You could draw a vertical line on cardboard or plywood as you described and align it with any degree of cant you want and line up the reticle to that.
Sure you can which won't be exactly correct since you scope is setting 1.5-2" above your bore

It will still be approximation which will always be less accurate than plugging the numbers into your handy, dandy ballistics app.

You can spend a great deal of time fiddling with it and get awfully close but it will still never be as accurate as doing the math, and little more accurate than just adjusting your hold on target if at all.

It is simply much easier and more accurate to set things up right from the start than it is to do anything like this.
 

WildRose

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I disagree with you on the zero range impacting cant error. Imagine using a lazer bore sighter at 1000 yards to show you where the barrel is aimed. That lazer will be 10-15 feet above your point of aim once you dial elevation for 1000 yards. Now cant your scope left and right and watch the lazer move horizontally with respect to your point of aim. Cant error is a function of the misalignment of bore axis and line of sight. As a test, take a gun that's zeroed at 200 yards and shoot it canted 90° clockwise. I guarantee you won't hit the bullseye. Rather you will hit several inches to the right.

I'll have to think about the windage + cant scenario for a bit :D
I'd like to see the laser bore sight that can be used on a rifle that would reach 1000yds ... .:)
 

MontanaRifleman

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I disagree with you on the zero range impacting cant error. Imagine using a lazer bore sighter at 1000 yards to show you where the barrel is aimed. That lazer will be 10-15 feet above your point of aim once you dial elevation for 1000 yards. Now cant your scope left and right and watch the lazer move horizontally with respect to your point of aim. Cant error is a function of the misalignment of bore axis and line of sight. As a test, take a gun that's zeroed at 200 yards and shoot it canted 90° clockwise. I guarantee you won't hit the bullseye. Rather you will hit several inches to the right.

I'll have to think about the windage + cant scenario for a bit :D

In you're example the bore is the zero point so it doesn't apply to zero points down range at a 100, 200 or 300. If zero'd @ 200, with rifle already canted to correct for spin drift, the bullet's POI and POA will be the same although the plain of the bullet's and the sightline will be different.... they meet at the zero point and from there diverge. The distance that happens at will detrmine how much they diverge down range along with the amount of cant.

If you canted the rifle over 90* with the scope to the side, your windage and elevation reticles switch roles. You can still zero to 100 or 200 yds but past that, the bullet will diverge left or right of line of sight because the scope and bore are not in the same vertical plain. It is an extreme example of what I said above.

Remember, to zero a rifle is to align the the POI and POA to be the same at a given point. If the POI and POA are not the same, the rifle is not zero'd.
 

MontanaRifleman

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Sure you can which won't be exactly correct since you scope is setting 1.5-2" above your bore

It will still be approximation which will always be less accurate than plugging the numbers into your handy, dandy ballistics app.

You can spend a great deal of time fiddling with it and get awfully close but it will still never be as accurate as doing the math, and little more accurate than just adjusting your hold on target if at all.

It is simply much easier and more accurate to set things up right from the start than it is to do anything like this.

I agree that doing the math is better. I'm just saying that is possible to fairly accurately set a cant. By the time you get done torquing down all the screws, you're lucky to be within a half degree of what you want anyway. 1 degree of cant is not going to amount to a lot of POI shift down range and that amount will also depend on how far down range you zero. The closer you zero to the target down range, the less the cant will affect the POI.
 

RTK

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If you canted the rifle over 90* with the scope to the side, your windage and elevation reticles switch roles. You can still zero to 100 or 200 yds but past that, the bullet will diverge left or right of line of sight because the scope and bore are not in the same vertical plain. It is an extreme example of what I said above.
.

Do you have a formula for degrees cant vs moa at distance?
 
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