Scope Levels- Why?

[Philward]

Does this make sense?View attachment 191257

At some point your canted rifle will still be zeroed, bullet will intersect point of aim, you just won't know exactly where it is.

 

[antelopedundee]

Does this make sense?View attachment 191257

No and it should be obvious why. If you've installed your scope properly it should be fixed to the rifle and not turn when you cant the rifle. Your top half of your diagram should look like this. The scope doesn't rotate in the rings when you cant the rifle as your diagram shows. It's still aligned with the bore just like it was when it was perfectly vertical.

A rifle canted to 45 degrees won't shoot to the same POI as it was at perfect vertical but it should shoot to the same point if consistently canted to 45 degrees. Just like consistency of case preparation and loading technique, consistency of hold is the key to shooting tight groups.

Why not get a quality made level like I showed earlier and put it on a Pic rail? That would allow you to "level" the rifle. If you use 2 piece bases that won't work.

 

[J E Custom]

The way I compensated for spin drift at 1000 yard matches was to add 1 MOA to my windage above the windage needed unless the wind was from a different direction, then I could subtract the 1 MOA and it would be very close (effects of Wind is very hard to calculate precisely, so If I input the necessary spin drift I was always close enough to get a first shot hit on the target and with two siter's it was easier to get on.

I also kept very good notes in my match book that verified the amount of spin drift was very close for my load. another good thing about getting everything leveled and indexed if for some reason the POI did not closely match the windage setting, it told me that ether my position was wrong or my wind dope was flawed.

To shoot your best you must eliminate as many built in errors as possible. and work on the human ones.

J E CUSTOM

 

[Philward]

Everyone must realize that the rifle "and" the scope must be level to each other. The line of bore and the line of site form a triangle and the hypotenuse must be vertical to the line of bore (The base of the triangle) this triangle Must be vertical to avoid error. If ether one is not level with the other. The whole exercise is a wast of time.

When setting up a scope level you must first level the rifle. (The guide rails are one of the ways to get the rifle level) Then level the recital Optically, or with a plum line, And then install the scope level and verify that the other levels are still correct and set the scope level. the scope level should be the last to set.

Then if you wan't go one step farther, go to the range and fire a 3 shot group at a vertical line at 100 yards and adjust the recital for 200, 300, 400, 500, 600 and so on firing 3 shots and aiming at the same point of aim. find the center of each group and draw a line through the center and if it is not vertical it will be an indication that something is not right.

Don't forget Spin Drift will effect the windage depending on the right or left hand barrel twist. But it will have little effect at closer distances. 600 to 1000 yards+ it will become obvious. (A good rule of thumb is about 1 MOA at 1000 yards.

J E CUSTOM

This would be the same as French tuning or walk back tuning in archery.

 

[Mram10us]

There is always the possibility my math is wrong; be happy to send my Excel file if someone wants it.

Well, only if you shoot one hole groups at 800 - if your groups are the width of the paint can any error (cant, wind call, etc) creates the probability of a miss. Wait...is that spray paint or Sherwin-Williams?

But like I said, the difference in the rifle canted/scope leveled are not as large as I would have thought.

Any time I do math I always like to remember the old joke: What is the difference between an engineer and an accountant? Answer: the accountant knows he isn't an engineer. (Accountants think that is pretty funny since engineers think accounting is "just math.")

Here is a decent write up. I didn't read it all though.

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Bryan Litz confirms Tubb's observation. Bryan tells us that, as a general rule of thumb (for common cartridges), a 1° cant will produce five (5) inches of lateral displacement at 1000 yards. Thus, if you cant your rifle just 8°, the POI would move 40″ from the center of the target, putting the shot off the edge of a 72″-wide target.

 

[An Idahoan]

Bryan Litz confirms Tubb's observation. Bryan tells us that, as a general rule of thumb (for common cartridges), a 1° cant will produce five (5) inches of lateral displacement at 1000 yards. Thus, if you cant your rifle just 8°, the POI would move 40″ from the center of the target, putting the shot off the edge of a 72″-wide target.

This is for a canted reticle, while not commenting on bore/optical axis relationship.

 

[LRNut]

Here is a decent write up. I didn't read it all though.

You are being redirected...

Bryan Litz confirms Tubb's observation. Bryan tells us that, as a general rule of thumb (for common cartridges), a 1° cant will produce five (5) inches of lateral displacement at 1000 yards. Thus, if you cant your rifle just 8°, the POI would move 40″ from the center of the target, putting the shot off the edge of a 72″-wide target.

My last post was for the rifle canted but the scope reticle leveled. When I posted about the rifle/scope combo canted, I used JBM Ballistics and entered cant angles; that is where I came up with .1 MOA per deg of cant. But I will be the first to admit that sounds too little; if I cant at 800 I definitely see a large horizontal error (just go out and try it).

I once wrote a story about canting for The VARMINT HUNTER mag in which I used a protractor and two scope levels to measure various cants and their affects at 700 yards. There was definitely a difference.

As for spin drift, Bryan Litz measured it with two different rifles, identical in every way except one was left twist and the other right; he shot alternating shots and then used the difference between the groups to develop his formula for spin drift. The SIG Kilo calculates spin drift as well as aerodynamic jump. My hit rates at LR have gone way up since I got this; kicks the BR7's butt.

As J E Custom said, there are enough unknowns that I want to be sure I obviate the ones I can. I use a level simply to rule out cant. If a bullet hits to the right more than I thought it would, I know it was probably a bad wind call (esp if the second one does too). Without a level, I would be wondering if it was a cant error.

 

[Mram10us]

My last post was for the rifle canted but the scope reticle leveled. When I posted about the rifle/scope combo canted, I used JBM Ballistics and entered cant angles; that is where I came up with .1 MOA per deg of cant. But I will be the first to admit that sounds too little; if I cant at 800 I definitely see a large horizontal error (just go out and try it).

I once wrote a story about canting for The VARMINT HUNTER mag in which I used a protractor and two scope levels to measure various cants and their affects at 700 yards. There was definitely a difference.

As for spin drift, Bryan Litz measured it with two different rifles, identical in every way except one was left twist and the other right; he shot alternating shots and then used the difference between the groups to develop his formula for spin drift. The SIG Kilo calculates spin drift as well as aerodynamic jump. My hit rates at LR have gone way up since I got this; kicks the BR7's butt.

As J E Custom said, there are enough unknowns that I want to be sure I obviate the ones I can. I use a level simply to rule out cant. If a bullet hits to the right more than I thought it would, I know it was probably a bad wind call (esp if the second one does too). Without a level, I would be wondering if it was a cant error.

Not shooting down your math. Like is said, I haven't done it, just bringing up this article to show guys smarter than me that think cant is important

 

[An Idahoan]

LRNut,

I'll take whatever excel doc you're using. We can compare notes. I want to be able to explain well, but without a 3D modeling software to video output, it is difficult. I'm sending you a PM with my email address. I hope no one sees what I am writing and thinks I think cant is unimportant. Reticle cant is super important. So much so that a bubble level is vital.

Paul

 

[jimbires]

This is the first post I've read where anyone said anything about aligning to the bore of rifle. It's the starting point I would think, and everything should be based off that. JE Custom may have mentioned it.

Can spin drift be adjusted out with a windage adjustable base, or is it an exponential change the further you go out?

reply #8 has a couple links worth reading . tall target , and cant .

spin drift increases as the distance gets longer . if you made a permanent adjustment you would be shooting to the left at close range . assuming a right twist barrel . would also need more correction at longer distances than you originally corrected for .

 

[LRNut]

Not shooting down your math. Like is said, I haven't done it, just bringing up this article to show guys smarter than me that think cant is important

Don't get wrong; I agree. But I would also

No and it should be obvious why. If you've installed your scope properly it should be fixed to the rifle and not turn when you cant the rifle. Your top half of your diagram should look like this. The scope doesn't rotate in the rings when you cant the rifle as your diagram shows. It's still aligned with the bore just like it was when it was perfectly vertical.

A rifle canted to 45 degrees won't shoot to the same POI as it was at perfect vertical but it should shoot to the same point if consistently canted to 45 degrees. Just like consistency of case preparation and loading technique, consistency of hold is the key to shooting tight groups.

Why not get a quality made level like I showed earlier and put it on a Pic rail? That would allow you to "level" the rifle. If you use 2 piece bases that won't work.

Antelope: there are now two discussions going on; one is for cant due to not having a level, and the other is for the question of "does the rifle need to be level the same time the scope is level?" I concluded the drawing he created was illustrating the later. You are illustrating the former.

 

[antelopedundee]

Thanks for the math! Is there any error straight up-straight using your calcs?
The 45 degree was a stupid statement-comparison, but I feel if someone wants to cant their stock 2-3 degrees for comfort, level the scope to accommodate, no ill effects. Canting the scope 3 degrees a whole different issue.
I am not one to tell people they cannot shoot within an inch at 800, but an inch off at 800 still destroys a paint can or anything bigger for that matter.

Or just adjust windage and elevation to allow for 3 degrees of cant assuming that you can maintain the 3 degrees consistently.

 

[milo-2]

Or just adjust windage and elevation to allow for 3 degrees of cant assuming that you can maintain the 3 degrees consistently.

I have a story on that, one day 7 of us were on the firing line, friendly get together. We had steel to 1330. All the targets after 300 on the half mark(350 etc..) were head bangers, 6x9" head, 12x16" body, the goal was the head. Left wind, nothing serious, finally someone missed and asked for a wind call, the first response was something like 2 moa right, others either in moa or mils was say 1 moa left. At 950, the right wind guy hit the head, like he had all previous targets, I asked his wind hold, he was now at around 2.5moa right hold in a left wind. I had to stand up and go see what he was doing, sure enough, his rifle was folded over to the left, as he was dialing both elevation and right wind, somehow his vertical was matching up, and whatever his cant was he was correcting it by holding right. At 1K he was done, no longer effective. We explained it, straightened his system up and told him to stay level and follow our wind calls, he made hits to 1050 after the correction, nothing past. No one was there to really coach him, we were there for fun, BBQ and shoot, poke fun at one another. Gave him something to ponder on his drive home. I was lost on how he did it, a 6" wide target at 700 is no walk in the park, yet he did it all the way to 950.
Forgot, told him to get a level also.

 

[LRNut]

That story I wrote for the The VARMINT HUNTER Mag is on a scope level website; I copied and pasted the picture of the setup I used to measure cant angles. What I did was rotate the gun to different angles using the protractor, then adjusted the second level so it was level - that way I could shoot with the same cant.