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Leveling the Scope Reticle for Long Range Rifles

 
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  #29  
Old 02-18-2013, 12:50 PM
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Re: Leveling the Scope Reticle for Long Range Rifles

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Originally Posted by shortpants View Post
Question??? Do you recommend shooting a plumbline test after using the alignment tool you sell to verify results? It seems the plumbline is the most accurate way to eliminate errors so why not just skip the alignment tool and shoot the plumbline to begin with? 6 or even 12 rounds is still cheaper than the alignment tool in most cases. The exception would be if you have more than a few scopes to worry about. Am I on the right track or did I miss something? No disrespect meant towards the alignment tool just wondering if its worth buying for someone like myself who only owns a couple of scoped rifles? Guess I need more rifles!!!
That's why I included the live fire method in the article, as well as a number of different reticle alignment tools. Different strokes for different folks.

To get the reticle aligned accurately using method 1, you need to fire at least three shot groups to accurately locate the point of impact. If you want to keep the round count down to 12 (four groups) or less, you will need to get the reticle alignment close before you start. That means using one of the alternative methods 4 or 5. If you already have the tools for those methods, then you're good to go.

I assume that you're using an anti-cant indicator. If not, your groups at 15-30 MOA elevation will probably be too large for long range shooting.

If you find that the first group fired at 15-30 MOA elevation is less than 1" from the plumb line, then you're done and it only cost you six rounds of ammunition. However, if the group is more than about 1" from the plumb line, you should re-align the scope. This is where the round count starts to go up.

Was the scope reticle canted or was the rifle canted, or both? That is, the scope reticle could be misaligned, or the anti-cant indicator could be misaligned, or both could be misaligned. By how much should you rotate the scope and/or anti-cant indicator to correct the error? Most folks will be cautious and try to rotate the scope just a degree or two at a time. How can you tell 1 degree of rotation when you're looking down at the scope? It's easy to get confused and rotate either the scope or anti-cant indicator in the wrong direction. Sorting all this out at the range could easily cost you half a day and a box of ammunition.

Generally, you don't need to use the live fire method to check reticle alignment after using the RingTrue alignment tool. I occasionally check the alignment of scopes using the live fire method, after I used the RingTrue tool to align the reticle and anti-cant indicator. I haven't found one case in which the cant was more than 1 degree. That's good enough for long range shooting.

The only exception I can think of would be if your rifle has a large boresight misalignment. For example, if you found that a large windage offset (>10 MOA) from the optical center was needed to optically align your reticle to the bore. Another possibility is if you optically zeroed the reticle to the bore, and then found that the point of impact was off more than about 16 MOA to the left or right. That would indicate that the boresight alignment is off due to barrel vibration. In either case, you would then have a residual reticle alignment error that could cause a significant canting error. Such large boresight errors are not common, but in my experience do happen about 20% of the time for high volume production rifles.

And yes, you need more rifles. Len at Long Range Rifles can help you with that problem.
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  #30  
Old 02-18-2013, 02:45 PM
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Re: Leveling the Scope Reticle for Long Range Rifles

That's a great answer, thank you very much! Whichever method used I would think it would make more sense to align the crosshair first then mount the anti can't device. I would not attempt to try and do them at the same time. I will be making a purchase from you very soon!
Thankyou,
Jason
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  #31  
Old 02-18-2013, 11:17 PM
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Re: Leveling the Scope Reticle for Long Range Rifles

Bruce,

Sir, would you mind checking your shop email for a message from me please. It's difficult for me to call your shop because of the almost 12 hr time diff. between where I am and CA.

I really appreciate your articles and advice. Thanks for taking the time to teach us old dogs new tricks!

Thanks Sir.
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  #32  
Old 02-19-2013, 01:46 PM
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Re: Leveling the Scope Reticle for Long Range Rifles

DocB,

I found your email and just responded. Email seems a little flaky right now. PM me if you did not receive it.

Bruce
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  #33  
Old 02-20-2013, 01:36 AM
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Re: Leveling the Scope Reticle for Long Range Rifles

Bruce, I was watching Best of the West the other night. The guy was talking about spin drift and noted at 1000 yards the bullet in his right twist gun was moving to the right 5" or so. I think he indicated he was shooting a 180 grn 7mm load. He canted the scope to the left 6 degrees I believe and stated for that particular load, it compensated for spin drift at a 1000 yards. To compensate for spin drift in a right twist barrel, I've always heard you want to sight your gun in to the left of center. Which method do you think is more accurate to address spin drift?
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  #34  
Old 02-20-2013, 03:58 PM
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Re: Leveling the Scope Reticle for Long Range Rifles

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Originally Posted by Triple BB View Post
Bruce, I was watching Best of the West the other night. The guy was talking about spin drift and noted at 1000 yards the bullet in his right twist gun was moving to the right 5" or so. I think he indicated he was shooting a 180 grn 7mm load. He canted the scope to the left 6 degrees I believe and stated for that particular load, it compensated for spin drift at a 1000 yards. To compensate for spin drift in a right twist barrel, I've always heard you want to sight your gun in to the left of center. Which method do you think is more accurate to address spin drift?
Aiming to the left introduces a linear aiming offset vs range. The spin drift effect is not linear or quadratic with range, but is even stronger than quadratic. Spin drift has nearly the same effect as canting, in terms of horizontal offset vs range.

So, canting the rifle is a good approach for correcting spin drift, especially if you are using a bullet drop compensated turret. It is also perfectly acceptable to simply calculate the spin drift, and factor that correction into your firing solution. Many ballistic calculators will do that automatically. The ballistic calculator will also correct for Coriolis, which can be nearly as large as spin drift.

A spin drift offset of 5-7 inches at 1,000 yds is about right for that round. A 6 degree cant seems way too much to correct for that spin drift, however. A 1 degree cant would be close to the right angle. To accurately calculate the correct cant angle to compensate for spin drift, you would need to know the details of bullet length, rifling twist rate, ballistic coefficient, optical sight height, etc.

It goes without saying that accurately correcting for spin drift by any means is not trivial. To hold any cant angle accurately (less than +/-0.5 degree of cant error), you would need a properly boresighted scope, and an accurately aligned reticle/turret and anti-cant indicator.
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  #35  
Old 02-20-2013, 04:38 PM
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Re: Leveling the Scope Reticle for Long Range Rifles

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Originally Posted by CanardNoir View Post
I'd call it the outer limit of short range.

Anything over about 350 yards remains a difficult shot for most of the rifle shooters I have known.

A friend in South Dakota built a .243 Win with a all of the really long-range bells & whistles you could want on a shoulder rifle. And he has long since quit taking shots under 500 yards.

One afternoon on his family's ranch, with his ballistic calculations and no wind, I consistently hit a 10"-dia. steel plate at a half mile.

And to me, that was really long range!
Since I've never attempted a shot out past 200yds at the rifle range(the longest distance they have ) when looking thru my range finder at 300,400, and out to 500 yds in our clearcut it's intimidating once I look at those distances with the naked eye(eye glasse's).

After reading most all of this thread I was concerned that my level level level kit was an obsolete tool for distances out to 300 yds, after all thats what I purchased the kit for. So as not to cheat myself of possibly missing the deer of a lifetime due to an unlevel scope. All three were unlevel.

Ballistics change dramactically from what I've read on ballitics tables for my rifles and the type bullets and their weight , 300yds seems to be the longest distance before a bullet starts to lose energy and start dropping like a dead goose. From what I've read here an unlevel scope will only compound to the problem.

THere is a range near me that I found on the internet that says they have a 900 meter range. I plan to visit and see if my rifles and 300yds like each other.
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