Leveling the Scope Reticle for Long Range Rifles

[bruce_ventura]

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.

 

[shortpants]

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

 

[DocB]

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.

 

[bruce_ventura]

DocB,

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

Bruce

 

[Triple BB]

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?

 

[bruce_ventura]

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.

 

[ItchyTF]

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.

 

[CRaTxn]

Before you get too crazy about your ability or lack thereof to hold a rifle level...take a look at YouTube Long Range Blog 56 ...it is 5 mins viewing time. or copy paste & click
http://www.youtube.com/resultssearc....0.0.0.91.171.2.2.0...0.0...1ac.1.hgVYd_0yRSE

Your vestibular senses [seat-of-the-pants orientation in space] are better than one might think. In USAF Pilot Training we utilized the Barany acceleration/decelerattion Chair to trick the semi-circular canals of the inner ear...kind of UNcaging your gyro...pretty easy with eyes closed but, once you get a look at the horizon your body can get pretty darn good SA [situational awareness]...actually your tolerances are better than the manufacturing tolerances for some spirit levels !

 

[gillettehunter]

I bought a Huskemaw scope last yr and took it in to Best of the West to install. They told me that they canted it about 2 to 2 1/2 degrees to account for spin drift. The segment on TV that someone was commenting on said they use 2 degrees if I remember it right. Bruce

 

[bruce_ventura]

Before you get too crazy about your ability or lack thereof to hold a rifle level...take a look at YouTube Long Range Blog 56 ...it is 5 mins viewing time. or copy paste & click
http://www.youtube.com/resultssearc....0.0.0.91.171.2.2.0...0.0...1ac.1.hgVYd_0yRSE

Your vestibular senses [seat-of-the-pants orientation in space] are better than one might think. In USAF Pilot Training we utilized the Barany acceleration/decelerattion Chair to trick the semi-circular canals of the inner ear...kind of UNcaging your gyro...pretty easy with eyes closed but, once you get a look at the horizon your body can get pretty darn good SA [situational awareness]...actually your tolerances are better than the manufacturing tolerances for some spirit levels !

I watched the video a few times. The vlogger attempted to show that in the presence of a visual spatial reference (mildot reticle against a natural scene), he could reproducibly return to the same inclination within 0.3 degree. His experiment was flawed, however, because the digital inclinometer was not oriented perpendicular to the rifle barrel. It was rotated about 45 degrees, apparently so that the camera could see the display and the vlogger's face without putting the camera in front of the muzzle. His measurements of canting repeatability were probably lower than the actual repeatability.

The vlogger seemed to be mainly concerned about canting error changing his point of impact between shots. That's a valid perspective if your primary concern is about group size. However, long range hunters are primarily concerned about cold bore, first shot accuracy.

Therefore, in the context of long range hunting, canting error is primarily an issue of angular accuracy. Reproducibility is an important factor too, but becomes moot if the accuracy is poor. The vlogger did not say anything about the accuracy of sensing true vertical, even though he had a digital inclinometer and could have done that experiment too.

Certainly, with an accurate spatial reference, like the horizon, surface of water, etc., a person can align a horizontal reticle line to true horizontal with reasonable accuracy. However, long range hunters don't generally have such good spatial references.

Tests have proven that without the benefit of a true visual horizon line as a spatial reference, humans are not very good at determining true vertical. In a dark room, without any spatial reference, a healthy person in an upright sitting position can determine true vertical to within +/- 3 degrees. In this test the person is relying solely on vestibular senses and proprioceptive inputs (skin, muscles and joints) for balance. Put that person in a prone position on uneven terrain, tilt the head ~15 degrees in a cheek weld, and throw in a bunch of visual scene clutter, such as sloped terrain, trees, etc., and the accuracy of determining true vertical is going to be much worse.

 

[paphil]

I think we are making mountains out of mole hills! The key is understanding that those long range compensated shots are completly dependant on the scope being perfectly vertical. The angle of the gun can be canted left or right quite a bit with no effect as long as the scope is vertical. Everyone holds their gun differently and in my opinion , it is more important to hold the gun comfortably and set the scope vertical . Yes the next guy on the gun will say the scope is crooked but if it is equiped with a level, it will shoot the same group if he pays attention to the level. There is nothing worse than setting someone up for a shot at long range and they forget to look at the level. If the gun comes up comfortably, it will be very close to level . Yes, spin drift plays a critical factor and when we do the scope set up on a 100 yard target, the scope is canted left about 2 degrees. I shoot a 100 yard group on the line and then dial up to 1000 yards and then want the group to be between .75 and 1 inch left of the line. Anyone who shoots longrange varmets will understand . With no wind, gun is dead on. right hold and left hold are the same for the same wind. Before, with the scope perfectly vertical, 2 mph wind from the left required a 2 MOA hold, same wind from the right required no hold. Just a small thing that makes life easier. I still sight guns in the old way. I take out the bolt and line up on a 25 yard target by eye. Two shots at that target and then to the 300yard and two more shots and I'm dead on. The bend in the barrel doesn't matter much, it is nice if it bows up, giving you more elevation with your scope without shims, but once the bullet leaves the barrel it can only go straight. Most of these little things don't mean much unless you are shooting less than 1/2 MOA . It was a great article but over the head of most, but all valed points!

 

[DocB]

Hey Phil and Bruce, Just pokin my head up over a 'mole hill' in regards to a couple of question marks that popped up while reading this..

when we do the scope set up on a 100 yard target, the scope is canted left about 2 degrees.
Are you saying the scope is rotated counterclockwise 2 degrees or the base is angled off center 2 degrees?

I shoot a 100 yard group on the line and then dial up to 1000 yards and then want the group to be between .75 and 1 inch left of the line.
After you dial up to 1000yds, are you still shooting the same POA on the same 100yd target as the first group you fired?

And for the kicker.. why aren't barrels just manufactured with a left hand twist to counter combined coriolis and spin drift effects?

I've learned a lot from this thread, thanks everyone for taking the time to help us understand what's actually happening when we launch one downrange!



DocB

 

[CRaTxn]

I watched the video a few times. The vlogger attempted to show that in the presence of a visual spatial reference (mildot reticle against a natural scene), he could reproducibly return to the same inclination within 0.3 degree. His experiment was flawed, however, because the digital inclinometer was not oriented perpendicular to the rifle barrel. It was rotated about 45 degrees, apparently so that the camera could see the display and the vlogger's face without putting the camera in front of the muzzle. His measurements of canting repeatability were probably lower than the actual repeatability.

The vlogger seemed to be mainly concerned about canting error changing his point of impact between shots. That's a valid perspective if your primary concern is about group size. However, long range hunters are primarily concerned about cold bore, first shot accuracy.

Therefore, in the context of long range hunting, canting error is primarily an issue of angular accuracy. Reproducibility is an important factor too, but becomes moot if the accuracy is poor. The vlogger did not say anything about the accuracy of sensing true vertical, even though he had a digital inclinometer and could have done that experiment too.

Certainly, with an accurate spatial reference, like the horizon, surface of water, etc., a person can align a horizontal reticle line to true horizontal with reasonable accuracy. However, long range hunters don't generally have such good spatial references.

Tests have proven that without the benefit of a true visual horizon line as a spatial reference, humans are not very good at determining true vertical. In a dark room, without any spatial reference, a healthy person in an upright sitting position can determine true vertical to within +/- 3 degrees. In this test the person is relying solely on vestibular senses and proprioceptive inputs (skin, muscles and joints) for balance. Put that person in a prone position on uneven terrain, tilt the head ~15 degrees in a cheek weld, and throw in a bunch of visual scene clutter, such as sloped terrain, trees, etc., and the accuracy of determining true vertical is going to be much worse.

I watched the video a few times. The vlogger attempted[ AN ATTEMPT THAT HITS THE TARGET IS NOT AN ATTEMPT BUT A "PROOF">CR] to show that in the presence of a visual spatial reference[ IN MHO IF YOU DO NOT HAVE VISUAL REFERENCE YOU CAN NOT ETHICALLY SHOOT LRH BECAUSE THE TOF MEANS AN UNWANTED ANIMAL OR OTHER SAFETY FACTOR COULD MOVE INTO THE POI BY THE TIME OF BULLET STRIKE>CR] (mildot reticle against a natural scene), he could reproducibly return to the same inclination within 0.3 degree. His experiment was flawed, however, because the digital inclinometer was not oriented perpendicular to the rifle barrel[I DISAGREE HERE BECAUSE THE SENSOR WAS OVER THE BORE WHILE THE INDICATOR FACE WAS TURNED FOR SAFETY AS YOU MENTION--AWAY FROM THE MUZZLE>CR] . It was rotated about 45 degrees, apparently so that the camera could see the display and the vlogger's face without putting the camera in front of the muzzle. His measurements of canting repeatability were probably lower than the actual repeatability[OBVIOUS TO THE OBSERVERS EYES HIS REPEATABILITY WERE AS THEY WERE -AS WE ACTUALLY SEE-ON FLIM NO PARALYSIS-OF-ANALYSIS REQUIRED>CR].

The vlogger seemed to be mainly concerned about canting error changing his point of impact between shots. That's a valid perspective if your primary concern is about group size. However, long range hunters are primarily concerned about cold bore, first shot accuracy[HE HITS THE TARGET COLD BARREL(NORWEGIAN WOOD COLD) ON FILM...I GIVE THAT MORE CREDIBILITY THAN TYPE ON PAPER OR COMPUTER SCREEN>CR]

Therefore, in the context of long range hunting[IF YOU DON'T THINK THE TERRAIN IN THESE VIDEOS (MANY ON ACTUAL ROE DEER CULLING OPERATIONS) AREN'T REAL WORLD ENOUGH???I DON'T THINK RUGGED IRREGULAR MOUNTAINS & RIDGES FOR BACKDROP CAN BE ANY MORE PURE UNLESS AN ANIMAL DIES>CR], canting error is primarily an issue of angular accuracy. Reproducibility is an important factor too, but becomes moot if the accuracy is poor[WHERE IN THE YouTubes DO YOU SEE ANYTHING THAT COULD BE CONSTRUED AS "POOR">CR]. The vlogger did not say anything about the accuracy of sensing true vertical[THOMAS IS MULTI-LINGUAL BUT HIS BLOG IS VISITED BY MANY LANGUAGES THUS HE EMPLOYS A MIME'S GESTURAL BODY LANGUAGE TO CONVEY HIS INTENT..AND VERY WELL IF YOU READ THE RESPONSES BELOW HIS ART>CR], even though he had a digital inclinometer and could have done that experiment too.

Certainly, with an accurate spatial reference, like the horizon, surface of water, etc., a person can align a horizontal reticle line to true horizontal with reasonable accuracy. However, long range hunters don't generally have such good spatial references. [SEE MY REMARKS FOR LRH TOF AND SAFETY BELOW>CR]

Tests[WHAT TESTS ARE YOU REFERENCING..IN MY POST I SPEAK OF PERSONAL AND OBSERVED BARANY CHAIR CLASSES WITH THE USAF INSTRUCTOR PILOTS /CLASS ROOM INSTRUCTORS SUPERVISING>CR] have proven that without the benefit of a true visual horizon line as a spatial reference, humans are not very good at determining true vertical[ WHAT DID YOUR EYES TELL YOUR BRAIN ABOUT REPEATABILITY DURING AND AFTER YOU WATCHED BLOG #56/>CR][BRUCE MY DEBATE IS WITH THIS CONCEPT EXPRESSED AND REAL WORLD FILMED REALITY; I TRUST IT WILL GENERATE THOUGHT AND TESTING BY MANY WHO READ IT --SHOOTING YEA--YOU SHOULD BE VERY PROUD OF YOUR ART i.e. WRITING AS IT HAS ELICITED SEVERAL RESPONSES AND AFTER ALL ISN'T THAT THE POINT OF ALL THIS?]. In a dark room, without any spatial reference, a healthy person in an upright sitting position can determine true vertical to within +/- 3 degrees. In this test the person is relying solely on vestibular senses and proprioceptive inputs (skin, muscles and joints) for balance[I CONCUR 100%>CR]. Put that person in a prone position on uneven terrain, tilt the head ~15 degrees in a cheek weld, and throw in a bunch of visual scene clutter, such as sloped terrain, trees, etc., and the accuracy of determining true vertical is going to be much worse.

>>>>>>>>>><<<<<<<<<<
i certainly enjoyed reading the depth of theoretical analysis our scholar invested in the article. Likewise I have no wish to attack a LRH sponsor, especially one that can give the blind a lighted path to "some" illumination BUTT, though we may have all been created equal in the eyes of our lord... our lord did NOT create all our eyes nor vestibular senses equal. All I am saying is, IF you think you need this or any device...you probably do.
IF a serious LRH watched all 60 "V"logs of Thomas Haugland you will see Practical Precision Accuracy out to 1600meters NOT yards with production [though German and European ] rifles & optics. When one can and does on film hit specific rocks and subMOA steel targets repeatedly cold barrel first shot...that my boy is not shooting for group...it is field accuracy at its finest.Bruce if you think the tremendous accuracy displayed on the these YouTube Long Range Blog [start with#56] clips "vlogger's" trips to rugged windy intermountain hunting type terrain was merely "an attempt " then I request you do a short tutorial video of your "attempt" at displaying what you consider " proper angular accuracy".
You make some strange comments ..I THINK I CAN ADDRESS THEM BEST BY MAKING MY COMMENTS IN CAPS NEXT TO YOUR SPECIFIC REMARKS ABOVE...i.e. the rest of my post is imbedded above...IN CAP>CR

 

[bruce_ventura]

Phil,

Thanks for jumping in. My experience with spin drift is limited. I take it you put a 2 degree cant on the scope for all long range rifles, regardless of the specific BC, bullet length and twist rate. Do you have a method of setting that cant angle in the shop, or do you dial it in at the range using the live fire method?