Scope specs and ballistic chart accuracy...

[MinnMooney]

I have become a fanatic with the accuracy of turret adjustments and ballistic charts.

Let me explain : (0% - 22% correction factor w/various scopes)

Turret adj. accuracy -
Some (most) shooters assume that when they "dial in" 10 moa (or ") on their elevation turret that their bullet will hit 10 moa (or ") higher or lower at 100 yds. In the vast majority of scopes, this is just not the case. I go to great lengths with every new scope I buy to test and record the exact, actual adjustment value of it's 'clicks' as opposed to it's assumed value. I do this with the scope mounted or unmounted but always in an unmovable, clamped set-up. My surveyor's rod is 150' away and I take an initial reading with the turret all the way to the bottom (fully to the "Down" limit) and then take readings at every full rotation to the extreme "Up" limit. I know the extreme rod readings and the number of turret 'clicks' that I've turned. At that point it's easy to compare the two to get the "correction factor".
Example : Rod reading - 45" (90" @ 100 yds. OR 85.94 moa). Turret reading - 350 'clicks' @ 4 clicks per moa or ". Each 'click' = 24.56 moa or 25.714". So... I record on my cheat-sheet that if a range (ex. : 740 yds.) calls for 20 moa, I multiply the 20 by my correction factor 1.02 for moa (25/24.56). It calls for 20+1 click. Not much to worry about, right? But, what if the correction factor is 0.90 or - in the case of one of my semi-expensive ($550) scopes - 0.84 ?! In that extreme case, the turret adj would be 16+3 clicks. MAJOR difference at 740 yds. At 20 moa of turret, I would have hit at 23+3 moa or 29" high. Not even close for "1 shot - 1 kill".
This method (although time consuming at 1st) saves time and money in the long-run. It really shines when prairie dog shooting when I shoot hundreds of rounds a day and shoot 15-25 days per year.

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Ballistic chart accuracy -

I usually test my ballistic program in the field and adjust it accordingly. Here's how I do that :
I shoot 5-10 rounds at 100 yards through a chronograph for zero'ing and velocity. I then run a 'test' or preliminary ballistics chart using that bullet at that velocity. Five shots each at 200, 300 and 411 yds (my backyard range limit) are shot at gradually taller targets so I can hold at the top and measure actual drop from the 100 yard line-of-sight zero. I compare the acual drop at each yardage with the chart. If it isn't close enough for me then I "adjust" one or both of the factors that controls the arc like the ballistic coefficient (B.C.) or velocity (fps). In some cases, I have to adjust for multiple B.C.s at various velocities.
The end result is that I have a chart for that bullet, at that velocity & in those atmospheric conditions. The atmospheric data can be changed in a heartbeat after that with either a pocket PC or (in advance) a lap top with print-out.

WOW ! That took a while to write up.

I hope to get some comments back on my methods and if you are doing something similar.

 

[Art Eatman]

I'm just a hunter--deer, mostly, and prairie dogs plus the occasional coyote--so
I'm not particular. I just do my usual sight-in for two inches high at 100 yards and figure I'm good to 400, anyway. "Set it and forget it."

I guess I'd get persnickety if I were shooting long-range competition target at varying ranges during a match...

 

[bpl]

I sight in for 2-2.5" high at 100 yards and figure I'm basically good to 300 yards with no holdover.

 

[MinnMooney]

I just do my usual sight-in for two inches high at 100 yards and figure I'm good to 400, anyway. "Set it and forget it."

Exactly as I did for 45 years because my "long distance shot" was 200-250 yds. Five or six years ago, everything changed for me. Medium distance came to be 400-600 yds whereas "long" distance was 700-1000+ yds. (A friend of mine was in a .50 cal. club that I got to tag along with so I did some calculations for a course they'd set up that was 2.2 miles to a distant target. A near calm day. 1st shot : 5' low/left. 2nd shot : a "Hit" on the 4'x8' plywood target.) Very small errors translated into generous misses. It became the "little things" like the difference between moa and inches. That 5% difference is almost meaningless at a deer/elk/moose within 200, 300 or even 400 yards. But, at a 6" steel plate at 600 yards it's the difference between at "ping" and a dust spray. A prairie dog at 800 yards is a "not-even-close" if one doesn't do their homework on scope error and ballistic chart error.

But, Hey!, I'm an anal aeronautical engineer (Whoops, there I go being redundant again) so doin' the calcs and seeing the results is fun for me but I can see where it could be tedious and boring for some.

To each, their own...........

 

[jpwilly]

Great info. I always run the numbers and do some testing once I have found my accuracy load for a certain bullet. I only shoot the 308 and 30-06 at 400 or a little more yrds so far...it's pretty simple for me. But I do keep a ballistic chart handy so I have an idea of where I would be at 600 or more.

 

[MCMXI]

Some (most) shooters assume that when they "dial in" 10 moa (or ") on their elevation turret that their bullet will hit 10 moa (or ") higher or lower at 100 yds. In the vast majority of scopes, this is just not the case.

That's a sweeping statement right there! It may be true but how many brands have you tested? How many models within each brand? How many duplicates of each model? In other words, what's your sample size?

Your method is certainly interesting and I could do something similar by taping together sheets of graph paper and shooting at 100 yards. Not so much as to correlate ballistic data tables to rifle scopes but merely to see if my scopes are linear, accurate and repeatable. Do you only test for vertical error?

At present I'm much more concerned with precision than accuracy. Are my scopes REPEATABLE week in and and week out? I'm not so concerned that my comeups don't exactly match my ballistic table since those table values are a model and not absolute. The important thing to me is that when I dial in an adjustment, the reticle moves by the same amount every time, up, down, left or right. My PRH seems to be VERY repeatable based on shooting at 100Y, 200Y, 300Y, 400Y, 500Y, 600Y and 800Y. My 6.5-20X Leupold Mark 4 that I use for F-Class appears to be very good too. I don't own any "cheap" scopes (only PRH, Leupold Mark 4 and Zeiss Conquest) and so far I don't have much to complain about. You've got me thinking though ... I see some testing in my future. Confidence in one's equipment makes a HUGE difference.

 

[MinnMooney]

comment by 1858 (post #7) :

That's a sweeping statement right there! It may be true but how many brands have you tested? How many models within each brand? How many duplicates of each model? In other words, what's your sample size?

Hey Eighteen'r,
You're right about sample size. I have 38 scopes presently and 32 have been thoroughly tested and spec'd. I have records on 12 others that I've sold in the past couple of years so to answer you inquiry, I have tested/spec'd 44 scopes (only 3 were duplicates).
Brands?
Nikon Buckmaster (4 different models)
Nikon Monarch & Monarch X (5 different models)
Burris Signature (3 different models)
Burris FulField II (2 different models)
Bushnell Elite 3200 (3 different models but 5 scopes)
Bushnell Elite 4200 (4 different models)
Bushnell Elite 6500 (2 different models)
Simmons Aetec (2 different models)
Barska Swat/Tac 10-40x56
Tasco
Redfield (2 different models)
Leupold VX-3 & 3L (5 different models)
Leupold VX-L
Millett (3 different models)
Weaver Grand Slam & Super Slam (4 different models)

All scopes tested have cost under $1200 including 3 cheap scopes at about $120-$160. The $120 Tasco 6-24x44 had, bar-none, the most accurate turret settings that I have ever tested. Second most accurate were 3 Bushnell Elite 3200 10x40 scopes......... all with 0.5% error. Worst was a $380 Barska 10-40x56 "Swat/Tactical" (an otherwise great scope) with a 16% error. (If the chart called for 20 moa, I'd dial in 20x.84=16.8 moa and nail the target every time!)

My Bushnell Elite 6500 2.5-16x50 Mil-Dot is 3% as is my Leupold VX-3 6.5-20x50 LR which seems to be fairly common.

I have never owned nor used a really 'high-end' scope like U.S. Optics, Nightforce NXS, Schmitt-Bender or Zeiss Diavari. I'd love to run tests on any/all of those.

I run the numbers for both MOA & Inches and if one hits almost exact then I make a note of that and use that data (I have both on my cheat-sheets).
If both have errors then I always use MOA 'cause I really like using Mil-Dot reticles.

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Do you only test for vertical error?

Correct. Windage is art - not precise mathmatics.

You sound like a person with either a scientific or engineering background.

 

[MCMXI]

MinnMooney,
That's an impressive data set right there. It is a pity that you haven't tested some higher end optics such as Nightforce, S&B and Premier Reticles to name a few. Nightforce is well known for very repeatable (precise) adjustments but that doesn't necessarily mean accurate adjustments. Also, it'd be interesting to repeat the tests after x amount of use. It's one thing to make a scope with accurate and precise adjustments, but it's quite another to keep them accurate and precise with lots of use (recoil affects too). This is also where Nightforce has an excellent reputation. Regardless, you've got me wanting to test my PRH 3-15x50mm which is a $2,500 scope. I'm planning on buying the 5-25X56mm model in the next few months so such a test may affect my decision.

You sound like a person with either a scientific or engineering background.

Yes, I'm a researcher (mechanical engineer) and work mostly on military funded projects.

 

[xphunter]

What was the accuracy spread of the VX-3 LR/T's?

 

[Geno]

Very interesting thread!

Geno

 

[MCMXI]

MinnMooney, I've read your initial post a few more times and I think that your results lead to some important questions.

1. Since you're making your measurements at 50 yards (typically), how do you know that the errors measured are due to the adjustments and not parallax? Different scopes are set up to be "parallax free" at different distances.

2. Have you found the adjustment error to be linear over the range? If you take a reading with the reticle at one end of the adjustment range, and then take another at the other end of the adjustment range, and then compare # of clicks to elevation change in inches, you're averaging the error over the complete range. You do mention that you take a reading at every full revolution of the turret (15 MOA on Mark 4 M1 turret) so obviously you have data that can be plotted in Excel from which you could determine the linearity of the adjustments.

I ask the second question since I'm sure that many of us don't use the whole adjustment range on our scopes. For example, my F-Class rifle (.308 Win) currently has a Leupold Mark 4 6.5-20x50mm scope with M1 adjustments. I have a 20 MOA base and the rifle/scope are zeroed for 200 yards. From that setting I can dial down -25.25 MOA and up +50.75 MOA. Those are the extremes of my adjustment range. However, to adjust for 100 yards I only need to dial down -1.75 MOA and for 1000 yards I need to come up 32.00 MOA. So basically, my real-world usable range is only 33.75 MOA out of the available 76.00 MOA and that range is centered fairly close to the center of the total range (55% vs. 50%).

3. Have you found any trends among the scopes tested in terms of having + or - error?

4. Do you test all variable power optics on the maximum magnification?

 

[MinnMooney]

from xphunter :

What was the accuracy spread of the VX-3 LR/T's?

ANS.:

My Bushnell Elite 6500 2.5-16x50 Mil-Dot is 3% as is my Leupold VX-3 6.5-20x50 LR which seems to be fairly common.

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fron 1858 :

That's an impressive data set right there. It is a pity that you haven't tested some higher end optics such as Nightforce, S&B and Premier Reticles

I sure wish that I could afford such fantastic scopes. Maybe some day...
A few years ago I toyed with the idea of buying one great scope and using picatinny bases on all of my rifles so the 1 scope would mount on any of them. I found some basic flaws with that reasoning : 1.) Each change from 1 rifle to another would require an adjustment of the turrets so (w/o having to use tons of ammo for re-Zero'ing) record keeping would be critical. 2.) I would lose critical "Up" adjustment on some applications due to the mounts are not all exactly the same on various receivers. I might have to take up that valuable "Up" adj to re-Zero the scope/rifle. (I hope that I made that clear.)

Also, it'd be interesting to repeat the tests after x amount of use.

I have a few scopes that have seen quite a bit of service since I spec'd them but none have been on high recoiling rifles. One scope was just recently spec'd and is on a Rem. 700 in .300 Win. Mag. That scope has only been thru about 50-60 test rounds while I'm working up an accurate load for an up-coming elk hunt in CO. I'll keep that "spec. repeat" in mind for after it has gone through a couple hundred rounds.

1. Since you're making your measurements at 50 yards (typically), how do you know that the errors measured are due to the adjustments and not parallax? Different scopes are set up to be "parallax free" at different distances.

Excellent question (I KNEW you were engineering based!) :
Ans. : Most of my scopes have either "Side Focus" (a misnomer since it's really parallax adj.) or an adjustable objective bell and I'm careful to accurately adj them. Those w/o parallax adjustment receive extra attention to keeping my eye/sight-picture exactly centered so parallax becomes a non-factor.

2. Have you found the adjustment error to be linear over the range? If you take a reading with the reticle at one end of the adjustment range, and then take another at the other end of the adjustment range, and then compare # of clicks to elevation change in inches, you're averaging the error over the complete range. You do mention that you take a reading at every full revolution of the turret (15 MOA on Mark 4 M1 turret) so obviously you have data that can be plotted in Excel from which you could determine the linearity of the adjustments.

Ans. : You have hit on all of those criteria that I have asked myself over these past years. "Yes", I do have that data and have found that the vast majority of my scopes are fairly consistant thoughout the elevation range.
Before you ask it, I'll pre-answer what might be your next question.....
I have run into a perplexing problem with some cheap scopes. When turning the turret in the counter-clockwise direction (as if 'unscrewing' the turret), the crosshair ceases it's movement even the turret continues to turn for one or more rotations. You can see where this could be a major problem. Here's the strange thing : If the rifle/scope is zero'd and I turn the turret 6 ccw rotations, the new point of impact (POI) might only be equal to 4.5 rotations but it takes those exact 6 full cw rotations to get back to zero! In other words, you won't hit what you adjusted for but when you crank back to your original zero, you'll hit at your original POI. Go figure.

3. Have you found any trends among the scopes tested in terms of having + or - error?

Ans. : Yes. Almost all of the tested scopes over adjust. In other words, I have to use a "less-than-1.0" correction factor. In most cases it's 0.95 - 0.99. If my ballistics data calls for a 7.5 moa drop and my correction factor is 0.95, I'd adjust by 7.5 x 0.95 = 7.125 moa.

4. Do you test all variable power optics on the maximum magnification?

Ans. : No, not all but most. Some of my scopes are so clear, bright and sharp that I test at full and, possibly, half power. P.S. I've found no error between those two settings so I've since quit the redundant testing.

 

[MinnMooney]

from Geno (post 10) :

Very interesting thread!

Thanks