For years we have touted the advantages of Burris Signature rings, with polymer Pos-Align Inserts. Now this system is available in a beefier, heavy-duty ring system for tactical rifles. The new Burris XTR Signature Rings offer six (6) clamping bolts per ring plus strong, dual steel base-clamps that self-center on Weaver or Picatinny rails. These aluminum XTR Signature Rings provide strength and holding power, plus the key benefits of Pos-Align inserts. As impressive as XTR rings are — they aren’t that expensive, with 1″-diameter XTRs starting at about $90.00 per pair (30mm and 34mm XTRs cost a bit more).

The polymer inserts in Signature rings perform three key functions. First, the inserts provide full, uniform scope-to-ring contact, with no need for lapping. You get a very secure “grip” on your scope without ring marks. Second, the Pos-Align inserts can provide elevation “pre-load”. With eccentric (offset) inserts, you can raise the back of the scope relative to the front, gaining up to 54 MOA of built-in elevation, without the need for expensive tapered bases. Third, the offset inserts can be rotated clockwise or counter-clockwise to shift point of impact. This lets you zero your rifle easily while keeping the turrets in the center of their travel.

Burris XTR Signature Rings are offered in 1″, 30mm, and 34mm diameters, and three (3) different heights: 1″, 1.25″, and 1.5″. Each ring set includes two sets of concentric inserts and one set each of the following offset inserts: +/-5 MOA, +/-10 MOA, +/-20 MOA. These allow you to “pre-load” elevation and/or center up your cross-hairs.

– Pre-load Elevation. No need for expensive tapered bases for long-range shooting.
– Correct misalignment caused by off-center receiver holes.
– Correct for bases or rings being slightly off-center.

How to Pre-load Elevation
To add elevation, set the Pos-Align Offset Inserts to raise the rear of the scope and lower the front. As long as there remains sufficient clearance between the front objective bell and the barrel, Burris recommends lowering the front of the scope the most and raising the rear of the scope the least. The amount of actual elevation “pre-load” will depend on the ring spacing (see chart). In the illustration, with 4.75 inches between ring centers, a +/- 20 MOA pair in the front combined with a -/+ 5 MOA pair in the rear will yield +25 MOA of total elevation. (If the rings are positioned further apart, you’ll get less elevation pre-load.)

Using Inserts to Adjust Point of Impact in Any Direction
Although it is convenient and most understandable to refer to the ring inserts as a “bottom” or “top” insert, the inserts may be rotated to any angle within the scope rings. This allows the shooter to correct the point-of-impact in any direction. The drawings below show how the inserts can be rotated to induce both elevation and windage changes at the same time.

Product tip from Boyd Allen. We welcome reader submissions.

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:

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
6

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.

The photo above, taken on 10/16/2010 clearly illustrates the problem at PRGC as the early morning sun is from the left and front. Note the backlit flag and the direction of the shadows. As the sun continues to rise, it aligns itself right down the range towards the shooters. Apart from the glare, the bull is hard to see on the targets once they’re up because the light is coming from behind the target, not from the front. A very challenging set of light conditions which will worsen from now through February as the sun stays lower in the sky month by month.

Anti-Glare Filters from Art Neergaard
I recently spoke to Art Neergaard about this problem. Art manufactures a number of innovative products for rifle sights through his company ShootingSight LLC and he had an idea for me. The idea was simple in concept, a “donut” filter for the front sight with a hole in the middle so as not to darken the already dim bull and yet, it would cut the glare that otherwise enters the front sight. The picture at left shows the filter mounted on the sight. When you’re looking through the sights, there isn’t the large gap around the aperture, it’s actually a very close match. Sticking the camera right into the sight obviously changes the perspective a bit.

I wanted to evaluate the Centra Goliath 30mm sight on my new Palma tubegun. Since Art intended to make the filters for the 30mm size, this was a good time to begin that evaluation as well. My last match score with this rifle, five weeks ago before the light got bad, was a 600-42X, since then, I’ve had a couple of poor matches with other rifles as the light and glare have really troubled me. With the 600-42 as a “good condition baseline” with this rifle I was eager to see how the filters would work.

Art sent me a few items: two filters (one gray, one orange), and one filter-holder for them, as well as a fixed aperture cut in the same material as the filters, with a beveled edge like the ones available for many years for smaller sights. The filters are interchangeable in the holder and can be changed in a minute or so. The aperture, however, is fixed as the hole is drilled in a lathe after mounting the disc in the holder — this ensures perfect concentricity for the aperture.

Gray Filter Preferred
Arriving at the range, I mounted the high-contrast orange filter first and looked through it. Frankly, although it cut glare well, I hate the look of an orange world! A quick change of filter and another look through the sights showed a good, glare-free and natural-looking sight picture with the gray filter. At right is a photo that shows the relative glare-cutting effect of the gray filter.

Scores Improved with Anti-Glare Filtration
Shooting a good mid-range .308 load with Winchester brass, Federal primers, IMR 4064 (manufactured in 1960, just like me) and moly-coated Sierra 190 gr. bullets, the rifle showed it’s good breeding giving me a 200-12X, 200-15X and 200-14X for a 600-41X, my 22nd score of 600! Well, quite a dramatic improvement over the last couple of weeks when I struggled to shoot 590, and back to the score I shot five weeks ago when the light was still good. Hooray! So yes, I’m very satisfied with the concept of the filter with a hole in it. All the extraneous glare that was hurting my sight picture was gone and the bull remained unimpaired. Not that the bull was too good to begin with as all I can see is a fuzzy gray blob out there, but keeping the center unfiltered was better than some solid filters I’ve tried in the past.

Clear Rain Filters for Front Sights
Art plans to make clear donut filters to use as rain shields for shooters with a front lens in their sight. That would keep raindrops off the lens — especially the middle of the lens where a drop could destroy the shooter’s ability to see the bull properly.

Filter Works with Fixed & Variable Apertures
Although I intended to try the fixed aperture also, I ended up shooting the entire match with the filter and the Centra variable aperture. I’ll try to use the fixed aperture (photo at left) next week. The value of a fixed aperture shouldn’t be underestimated. It provides a lower cost way to use a 30mm sight, an important consideration given the current $175 price of the adjustable aperture. Perhaps just as important, the fixed aperture is something that should be in every high-end shooter’s kit in case of failure of the adjustable, which has been known to happen. If I were traveling across the country or around the world to a match, you can be sure there would be a set of fixed apertures of various sizes in my kit to back up the adjustable iris.

Art Neergaard
ShootingSight LLC
www.ShootingSight.com
eMail: shootingsight@nuvox.net
Phone: 513-702-4879