Burris Signature Rings with polymer inserts are an excellent product. The inserts allow you to clamp your scope securely without ring marks. Moreover, using the matched offset inserts you can “pre-load” your scope to add additional elevation. This helps keep the scope centered in its elevation range while shooting at long range. Additionally, with a -20 insert set in the front and a +20 insert set in the rear, you may be able to zero at very long ranges without using an angled scope base — and that can save money. (To move your point of impact upwards, you lower the front of the scope relative to the bore axis, while raising the rear of the scope.)
Insert Elevation Values and Ring Spacing
People are sometimes confused when they employ the Burris inserts. The inset numbers (-10, +10, -20, +20 etc.) refer to hundredths of inch shim values, rather than to MOA. And you need the correct, matched top/bottom pair of inserts to give you the marked thousandth value. Importantly, the actual amount of elevation you get with Burris inserts will depend BOTH on the insert value AND the spacing between ring centers.
Forum member Gunamonth has explained this in our Shooters’ Forum:
Working with Burris Signature Rings
Burris inserts are [marked] in thousandths of an inch, not MOA. To know how many MOA you gain you also need to know the ring spacing. For example, with a -20 thou insert set in the front and a +20 thou insert set in the rear, if the ring spacing is 6″, the elevation change will be approximately +24 MOA upwards.
Here’s how we calculate that. If you have a 2 X 0.020″ “lift” over a distance of 6 inches (i.e. 0.040″ total offset at 0.5 feet) that’s equivalent to 0.080″ “lift” over 12 inches (one foot). There are 300 feet in 100 yards so we multiply 0.080″ X 300 and get 24″ for the total elevation increase at 100 yard. (Note: One inch at 100 yards isn’t exactly a MOA but it’s fairly close.)
Here’s a formula, with all units in inches:
Total Ring Offset
——————– X 3600 = Change @ 100 yards
Ring Spacing
(.020 + .020)
—————– X 3600 = 24 inches at 100 yards
Ring Spacing: 6 inches
NOTE: Using the above formula, the only time the marked insert offset will equal the actual MOA shift is when the center to center ring spacing is 3.60″. Of course, you are not required to use 3.60″ spacing, but if you have a different spacing your elevation “lift” will be more or less than the values on the inserts.
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Based on its external appearance, a modern riflescope may seem simple. It’s just a tube with two or three knobs on the outside right? Well, looks can be deceiving. Modern variable focal-length optics are complex systems with lots of internal parts. Modern scopes, even ‘budget’ optics, use multiple lens elements to allow variable magnification levels and parallax adjustment.
A few seasons back, we had a chance to look inside a riflescope thanks to a product display from ATK, now called Vista Outdoor, parent of Alliant Powder, CCI, Federal, RCBS, Speer, Weaver Optics. The Weaver engineers sliced open a Weaver Super Slam scope so you can see the internal lens elements plus the elevation and windage controls. We thought readers would like to see the “inner workings” of a typical modern rifle scope, so we snapped some pictures. The sectioned Super Slam scope was mounted inside a Plexiglas case, making it a bit hard to get super-sharp images, but you can still see the multiple lenses and the complex windage and elevation controls.
Check out the details of the focusing and magnification rings near the ocular (eyeball) end of the scope. There is very fine machining and threading to make everything work properly. The ocular lens is the piece of glass that faces the shooter while he aims.
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In a helpful NSSF video, Ryan Cleckner explains why you normally should avoid canting your rifle — rotating it clockwise or counter-clockwise. Cleckner explains that canting the rifle in one direction or another will change the point of impact: “When you rotate the rifle, not only does the [POI move] in the direction that you’re rotated, [but] it also loses some of its elevation as it rolls down.” This, Cleckner explains, can make you miss on one side or the other:
Cant to the Left — You’re going to miss low and left.
Cant to the Right — You’re going to miss low and right.
In this video, starting at the one-minute mark, Cleckner shows the effect of rifle canting when engaging a 600-yard target. A few degrees of cant (either to the left or to the right), moves the shot POI completely off the steel silhouette target. The POI change occurs mainly because you are lowering (and laterally shifting) the scope sight-line relative to the bore axis, effectively changing your zero.
David Tubb has explained: “Every 1 degree you are off on a cant, is about six inches of difference laterally at 1000 yards”.
Position Shooting with Sling — Rifle Cant Considerations
Cleckner’s discussion assumes that the scope or sights are set to hit center with the rifle level and plumb. That works for most situations when shooting prone off bipod, front mechanical rest, or front sandbag. However, many sling shooters, including David Tubb and John Whidden, do tilt or cant their rifles slightly inward because this allows a more comfortable hold with sling, or allows better eye-to-sight alignment. Holding the rifle at an angle can work — but the angle of cant must be consistent for every shot. Canting the rifle is not a sin by itself. However, after you confirm your zero on your target, the degree of cant must be the same for EVERY shot. You must maintain that exact same degree of rotation on each shot or you will experience the shot POI movement Cleckner illustrates. Consistency is the key.
John Whidden, 5-time Nat’l Long Range Champion, holds a Palma rifle. John now shoots a match rifle with an Anschutz stock which he holds more upright, but still with some counter-clockwise cant. John also installed his iron sights at an angle so that the adjustments are correct (and plumb) even with his canted hold: “While it may not be obvious in the picture, the sights on my rifle are set up so that they’re straight vertical and horizontal while I hold the rifle canted. Making sure your adjustments (scope or sights) are vertical and horizontal is a critical piece of the pie.”
Inexpensive Dual-Diameter Scope-Mounted Bubble Level
The best way to avoid inconsistent rifle canting is to use a bubble level fitted to rail or scope. One very affordable and versatile product is the Jialitte Scope Bubble Level. This features a 30mm milled inside diameter, plus an inner insert ring so it will also fit 1″-diameter main tubes. The Jialitte unit is nicely radiused, and has a low profile in the middle. User reviews have been very positive. You could easily pay $35.00 or more for a 30mm scope level. This costs just $9.99 on Amazon.
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In a helpful NSSF video, Ryan Cleckner explains why you normally should avoid canting your rifle — rotating it clockwise or counter-clockwise. Cleckner explains that canting the rifle in one direction or another will change the point of impact: “When you rotate the rifle, not only does the [POI move] in the direction that you’re rotated, [but] it also loses some of its elevation as it rolls down.” This, Cleckner explains, can make you miss on one side or the other:
Cant to the Left — You’re going to miss low and left.
Cant to the Right — You’re going to miss low and right.
In this video, starting at the one-minute mark, Cleckner shows the effect of rifle canting when engaging a 600-yard target. A few degrees of cant (either to the left or to the right), moves the shot POI completely off the steel silhouette target. The POI change occurs mainly because you are lowering (and laterally shifting) the scope sight-line relative to the bore axis, effectively changing your zero.
David Tubb has explained: “Every 1 degree you are off on a cant, is about six inches of difference laterally at 1000 yards”.
Position Shooting with Sling — Rifle Cant Considerations
Cleckner’s discussion assumes that the scope or sights are set to hit center with the rifle level and plumb. That works for most situations when shooting prone off bipod, front mechanical rest, or front sandbag. However, many sling shooters, including David Tubb and John Whidden, do tilt or cant their rifles slightly inward because this allows a more comfortable hold with sling, or allows better eye-to-sight alignment. Holding the rifle at an angle can work — but the angle of cant must be consistent for every shot. Canting the rifle is not a sin by itself. However, after you confirm your zero on your target, the degree of cant must be the same for EVERY shot. You must maintain that exact same degree of rotation on each shot or you will experience the shot POI movement Cleckner illustrates. Consistency is the key.
John Whidden, 5-time Nat’l Long Range Champion, holds a Palma rifle. John now shoots a match rifle with an Anschutz stock which he holds more upright, but still with some counter-clockwise cant. John also installed his iron sights at an angle so that the adjustments are correct (and plumb) even with his canted hold: “While it may not be obvious in the picture, the sights on my rifle are set up so that they’re straight vertical and horizontal while I hold the rifle canted. Making sure your adjustments (scope or sights) are vertical and horizontal is a critical piece of the pie.”
Inexpensive Dual-Diameter Scope-Mounted Bubble Level
The best way to avoid inconsistent rifle canting is to use a bubble level fitted to rail or scope. One very affordable and versatile product is the Jialitte Scope Bubble Level. This features a 30mm milled inside diameter, plus an inner insert ring so it will also fit 1″-diameter main tubes. The Jialitte unit is nicely radiused, and has a low profile in the middle. User reviews have been very positive. You could easily pay $35.00 or more for a 30mm scope level. This costs just $8.79 on Amazon (Cyber Monday special).
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Burris Signature Rings with polymer inserts are an excellent product. The inserts allow you to clamp your scope securely without ring marks. Moreover, using the matched offset inserts you can “pre-load” your scope to add additional elevation. This helps keep the scope centered in its elevation range while shooting at long range. Additionally, with a -20 insert set in the front and a +20 insert set in the rear, you may be able to zero at very long ranges without using an angled scope base — and that can save money. (To move your point of impact upwards, you lower the front of the scope relative to the bore axis, while raising the rear of the scope.)
Insert Elevation Values and Ring Spacing
People are sometimes confused when they employ the Burris inserts. The inset numbers (-10, +10, -20, +20 etc.) refer to hundredths of inch shim values, rather than to MOA. And you need the correct, matched top/bottom pair of inserts to give you the marked thousandth value. Importantly, the actual amount of elevation you get with Burris inserts will depend BOTH on the insert value AND the spacing between ring centers.
Forum member Gunamonth has explained this in our Shooters’ Forum:
Working with Burris Signature Rings
Burris inserts are [marked] in thousandths of an inch, not MOA. To know how many MOA you gain you also need to know the ring spacing. For example, with a -20 thou insert set in the front and a +20 thou insert set in the rear, if the ring spacing is 6″, the elevation change will be approximately +24 MOA upwards.
Here’s how we calculate that. If you have a 2 X 0.020″ “lift” over a distance of 6 inches (i.e. 0.040″ total offset at 0.5 feet) that’s equivalent to 0.080″ “lift” over 12 inches (one foot). There are 300 feet in 100 yards so we multiply 0.080″ X 300 and get 24″ for the total elevation increase at 100 yard. (Note: One inch at 100 yards isn’t exactly a MOA but it’s fairly close.)
Here’s a formula, with all units in inches:
Total Ring Offset
——————– X 3600 = Change @ 100 yards
Ring Spacing
(.020 + .020)
—————– X 3600 = 24 inches at 100 yards
Ring Spacing: 6 inches
NOTE: Using the above formula, the only time the marked insert offset will equal the actual MOA shift is when the center to center ring spacing is 3.60″. Of course, you are not required to use 3.60″ spacing, but if you have a different spacing your elevation “lift” will be more or less than the values on the inserts.
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With the price of premium scopes approaching $3400.00 (and beyond), it’s more important than ever to provide extra protection for your expensive optics. ScopeCoat produces covers that shield scopes with a layer of neoprene rubber (wetsuit material) sandwiched between nylon. In addition to its basic covers, sold in a variety of sizes and colors, ScopeCoat has a line of heavy-duty 6mm-thick XP-6 covers that provide added security. CLICK HERE to review the full line of ScopeCoats on Amazon.
Triple-Thickness XP-6 Model for Added Protection
The XP-6 Flak Jacket™ is specifically designed for extra protection and durability. The 6mm-thick layer of neoprene is three times thicker than the standard ScopeCoat. XP-6 Flak Jackets are designed for tall turrets, with sizes that accommodate either two or three adjustment knobs (for both side-focus and front-focus parallax models). To shield an expensive NightForce, March, or Schmidt & Bender scope, this a good choice. XP-6 covers come in black color only, and are available for both rifle-scopes and spotting scopes.
The heavily padded XP-6 Flak Jacket is also offered in a Zippered version, shown at right. This is designed for removable optics that need protection when in storage. The full-length, zippered closure goes on quick-and-easy and provides more complete protection against dust, shock, and moisture. The line of XP-6 Scope Covers run $23 – $34 on Amazon.
Special Covers for Binos and Red-Dots
ScopeCoat offers many specialized products, including oversize covers for spotting scopes, protective “Bino-Bibs” for binoculars, rangefinder covers, even sleeves for small pistol scopes and red-dot optics. There are also custom-designed covers for the popular Eotech and Trijicon tactical optics.
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Forum member Jacob spotted this simple, but effective set of scope ring inserts on the Brownells Website. With these inserts, you can use a scope with 1″-diameter main tube in 30mm rings. Non-marring, matte black Delrin sleeves surround the scope tube so it can fit larger-diameter rings. Each sleeve comes in two parts for easy installation around your scope tube. This way you can use the same 30mm rings for all your scopes.
Ring Reducers are sold as front/rear kits. Cost is $16.99 for the Delrin 30mm to 1″ converters, item 084-000-091WB. There are also sets that reduce 30mm rings to 26mm, and 1″ rings to 3/4″ or 7/8″.
Note: These Brownells units simply function as plastic bushings. Unlike Burris Signature Ring inserts, they do not allow you to “pre-load” windage or elevation. If your rings are misaligned, the Brownells Ring Reducers won’t correct that problem.
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MIL-system scopes are popular with tactical shooters. One advantage of MIL scopes is that the mil-dot divisions in the reticle can be used to estimate range to a target. If you know the actual size of a target, you can calculate the distance to the target relatively easily with a mil-based ranging reticle. Watch this helpful NRA video to see how this is done:
Milliradian Definition and Yardage Ranging Formula
“MIL” or “Milrad” is short-hand for Milliradian, a unit of angular measurement. The subtension of 1 mil equals 3.6 inches at 100 yards or 36 inches at 1,000 yards. (In metric units, 1 mil equals 10 centimeters at 100 meters or 1 meter at 1,000 meters.) Knowing this subtension and knowing the size of the target (or a reference object near the target) allows the distance to the target to be estimated with considerable accuracy. The formula used to calculate range (in yards) based on MIL measurement is:
Height of Target in inches (divided by 36) x 1000, divided by the number of mils.
For example, if a 14″ tall target spans 3 mils from top to bottom, the distance is 129.67 yards calculated as follows: 14/36 x 1000 = 389, then divided by 3 = 129.67. You can also use a different conversion to find distance in meters.
Can You Estimate Range with an MOA-Marked Reticle? Yes You Can…
Reader Josh offers this handy advice: “It worth noting that the ability to measure range is not unique to mil-based systems. A MIL is just another unit for measuring angles, and any angular measurement will work. Considering that just about everybody knows that 1 MOA is about an inch per hundred yards, similar formulae can be developed for ranging with MOA marks. The advantage with mils is the precise relationship between units — the MOA-inch measurement is imprecise (being off by 0.047″) — so in principle MILs are a better unit”.
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Based on its external appearance, a modern riflescope may seem simple. It’s just a tube with two or three knobs on the outside right? Well, looks can be deceiving. Modern variable focal-length optics are complex systems with lots of internal parts. Modern scopes, even ‘budget’ optics, use multiple lens elements to allow variable magnification levels and parallax adjustment.
A few seasons back, we had a chance to look inside a riflescope thanks to a product display from ATK, parent of Alliant Powder, CCI, Federal, RCBS, Speer, Weaver Optics. ATK sliced open a Weaver Super Slam scope so you can see the internal lens elements plus the elevation and windage controls. We thought readers would like to see the “inner workings” of a typical modern rifle scope, so we snapped some pictures. The sectioned Super Slam scope was mounted inside a Plexiglas case, making it a bit hard to get super-sharp images, but you can still see the multiple lenses and the complex windage and elevation controls.
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Now this is smart — ZEISS has just introduced a series of precision scope rings with integral bubble levels. These new ZEISS Ultralight 1913 Mil-Spec Rings for Picatinny Rails are beautifully made, making them a smart choice for mounting all brands of quality riflescopes. The rings are currently offered in 30mm diameter (low, med, high) and 36mm diameter (med, high), with 34mm versions coming out in the very near future.
We like the craftsmanship on these Precision Rings — they are “micro-radiused” on the machined leading edges to ensure a non-marring design. That special design feature helps prevent annoying marks on your expensive scope. Along with the built-in anti-cant levels, these rings feature an integral bottom recoil lug. That helps ensure the rings align perfectly and hold securely even with the high recoil forces generated by big caliber, magnum rifles.
Though these Precision Rings are very strong, they are also relatively light-weight. Crafted from Mil-Spec 7075-T6 aluminum (Type III) these rings weigh just 4.4 ounces with screws for a 30mm low set. For durability, ZEISS UltraLight Rings feature a 30-micron hard, matte black, anodized finish. The ring sets ship with a nice hard case, which includes both T15 and T25 Torx driver bits. The Zeiss Ultralight 30mm Rings cost $179.99 while the larger-diameter 36mm rings cost $199.99
NOTE: These rings are designed for correct, Mil-Spec Picatinny rails (aka MIL-STD-1913 rail or STANAG 2324 rail). Some lower-cost “Weaver-type” rails may not be ideal. ZEISS states: “For optimum performance and flawless mounting, we strongly advise that you mount [these rings] on a high-quality 1913 Mil-Std specification rail[.]”
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Let’s say you’ve purchased a new scope, and the spec-sheet indicates it is calibrated for quarter-MOA clicks. One MOA is 1.047″ inches at 100 yards, so you figure that’s how far your point of impact (POI) will move with four clicks. Well, unfortunately, you may be wrong. You can’t necessarily rely on what the manufacturer says. Production tolerances being what they are, you should test your scope to determine how much movement it actually delivers with each click of the turret. It may move a quarter-MOA, or maybe a quarter-inch, or maybe something else entirely. (Likewise scopes advertised as having 1/8-MOA clicks may deliver more or less than 1 actual MOA for 8 clicks.)
Reader Lindy explains how to check your clicks: “First, make sure the rifle is not loaded. Take a 40″ or longer carpenter’s ruler, and put a very visible mark (such as the center of an orange Shoot’N’C dot), at 37.7 inches. (On mine, I placed two dots side by side every 5 inches, so I could quickly count the dots.) Mount the ruler vertically (zero at top) exactly 100 yards away, carefully measured.
Place the rifle in a good hold on sandbags or other rest. With your hundred-yard zero on the rifle, using max magnification, carefully aim your center crosshairs at the top of the ruler (zero end-point). Have an assistant crank on 36 (indicated) MOA (i.e. 144 clicks), being careful not to move the rifle. (You really do need a helper, it’s very difficult to keep the rifle motionless if you crank the knobs yourself.) With each click, the reticle will move a bit down toward the bottom of the ruler. Note where the center crosshairs rest when your helper is done clicking. If the scope is accurately calibrated, it should be right at that 37.7 inch mark. If not, record where 144 clicks puts you on the ruler, to figure out what your actual click value is. (Repeat this several times as necessary, to get a “rock-solid”, repeatable value.) You now know, for that scope, how much each click actually moves the reticle at 100 yards–and, of course, that will scale proportionally at longer distances. This optical method is better than shooting, because you don’t have the uncertainly associated with determining a group center.
Using this method, I discovered that my Leupold 6.5-20X50 M1 has click values that are calibrated in what I called ‘Shooter’s MOA’, rather than true MOA. That is to say, 4 clicks moved POI 1.000″, rather than 1.047″ (true MOA). That’s about a 5% error.
I’ve tested bunches of scopes, and lots have click values which are significantly off what the manufacturer has advertised. You can’t rely on printed specifications–each scope is different. Until you check your particular scope, you can’t be sure how much it really moves with each click.
I’ve found the true click value varies not only by manufacturer, but by model and individual unit. My Leupold 3.5-10 M3LR was dead on. So was my U.S.O. SN-3 with an H25 reticle, but other SN-3s have been off, and so is my Leupold 6.5-20X50M1. So, check ‘em all, is my policy.”
From the Expert: “…Very good and important article, especially from a ballistics point of view. If a ballistics program predicts 30 MOA of drop at 1000 yards for example, and you dial 30 MOA on your scope and hit high or low, it’s easy to begin questioning BCs, MVs, and everything else under the sun. In my experience, more than 50% of the time error in trajectory prediction at long range is actually scope adjustment error. For serious long range shooting, the test described in this article is a MUST!” — Bryan Litz, Applied Ballistics for Long-Range Shooting.
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Are you shopping for a long range optic? Unfortunately, it is pretty much impossible to “test drive” a half-dozen or more optics. Thankfully, there are some video reviews on the internet that are, for the most part, helpful. Pew Pew Tactical (PPT) recently did a lengthy comparison of nine long range scopes. For each model PPT examined clarity, eye relief, reticle design, parallax, and windage/elevation travel. For each optic PPT also provides short videos showing the operation of the controls. FULL PPT REVIEW HERE.
NINE Long Range Scopes Compared
1. Vortex Strike Eagle 4-24×50mm
2. Vortex Viper PST II 5-25×50mm
3. Leupold VX3i LRP 8.5-25×50mm
4. Leupold Mark 5HD 5-25×56mm
5. Burris XTR II 5-25×50mm
This is actually a pretty good video. The host, Joel, tests and compares the Leupold Mark 5 vs. the Athlon Argos. Joel considers a variety of performance categories including clarity, tracking, elevation travel, ergonomics, and reticle options. This video asked the question “Can a $400 scope hang with a much higher priced optic?” You might be surprised how well the Athlon actually did.
Kalibre 22 — High-End Tactical Optics Comparison
In this video, Todd Hodnett explains the pros and cons of different brands and types of scopes. Scopes tested include Horus, Leupold, Nightforce, Schmidt & Bender, and Vortex. He uses the scopes in the field, and actually does a pretty good job describing the pros and cons of each model.
Top 10 Reviews — Manufacturer Marketing Videos Compilation
This video covers ten different scope models, from budget to high-end. For the most part the scopes appear in cost order, with the more affordable optics first. This YouTube video is mostly pieced together from manufacturer marketing footage, but it does cover a wide variety of scope options.
Please note, the above video does has some actual review segments, but nearly all the content is provided by the scope makers. So the Top 10 rankings are somewhat arbitrary. Nonetheless it is handy to have ten scopes covered in a single video. In order of appearance, here are the ten scopes featured, with video time marks if you want to “fast forward” to particular models.
TEN Scopes In Order of Display
10. Burris Veracity Riflescope: 00:23
9. Vortex Viper PST Gen II Riflescope: 01:24
8. Nikon BLACK FX1000 Riflescope: 03:18
7. ATN X-Sight 4K PRO Riflescope: 04:29
6. Bushnell Engage™ Riflescope 06:00
5. Leica Magnus i Riflescope: 07:50
4. Nightforce ATACR 5-25x56mm F1 Riflescope: 08:29
3. Vanguard Endeavor RS IV Riflescope: 10:31
2. Leupold Mark 8 Riflescope: 12:33
1. Swarovski Z8i Riflescope: 14:21
Great Deals on Vortex Now
Looking for a great deal on a new scope? Leading vendor EuroOptic has a wide variety of Vortex Scopes at deeply discounted close-out prices now:
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With the price of premium scopes approaching $3400.00 (and beyond), it’s more important than ever to provide extra protection for your expensive optics. 
The heavily padded XP-6 Flak Jacket is also offered in a Zippered version, shown at right. This is designed for removable optics that need protection when in storage. The full-length, zippered closure goes on quick-and-easy and provides more complete protection against dust, shock, and moisture. The line of XP-6 Scope Covers run 
Reader Lindy explains how to check your clicks: “First, make sure the rifle is not loaded. Take a 40″ or longer carpenter’s ruler, and put a very visible mark (such as the center of an orange Shoot’N’C dot), at 37.7 inches. (On mine, I placed two dots side by side every 5 inches, so I could quickly count the dots.) Mount the ruler vertically (zero at top) exactly 100 yards away, carefully measured.
