GUNS Magazine June 2013 Digital Edition - Page 48

Modern Scop H JoHn barsness and-held laser rangefinders became available to shooters in the mid-1990s, changing riflescopes forever. When shooters could determine the exact range to distant targets, they started demanding more magnification and a wider range of repeatable adjustments. Both demands resulted in scope mounting problems our grandfathers never imagined. Today many of us crank our scope’s elevation adjustment up and down repeatedly, and sometimes expect the same of the windage turret. We also expect to have plenty of adjustment range even when the scope’s turned up to 20X or more when shooting our .300 Miracle Magnum out at 1,000 yards. One problem is keeping bigger scopes in place, especially on rifles chambered for more powerful cartridges. Other problems involve scope alignment with the rifle’s bore, plus reducing any strains on the scope itself, allowing adjustments to work consistently. Though the three problems are somewhat interrelated, let’s start by examining them separately. Back when we considered a 3-9X variable “big,” most scopes could be mounted on just about any factory rifle and be sighted-in without trouble. This was partly due to the relatively wide field of view, and partly because so many shooters used Redfield-type mounts, with the rear ring held in place by a pair of opposing screws. (These days Redfield-type mounts are made by a bunch of companies, including Burris, Leupold and probably some sweatshop in China, but Redfield invented them almost 100 years ago, when many scopes didn’t have internal windage adjustments.) Turning the screws provided some windage adjustment, so even if our 3-9X scope ran out of internal adjustments when sighting-in, we could fiddle with the screws and get our rifle on paper at 100 yards. Unfortunately, this popular mounting system isn’t the strongest in the world, despite what some shooters believe. If you look closely at the rear ring of a Redfield-type mount on rifles chambered for cartridges recoiling much more than the .30-06, you’ll often be able to see where the ring has slipped slightly between the windage screws. This is because the front ring, held by a dovetail slot in its base, takes most of the stress of recoil. While Redfield-type mounts work fine with average-size scopes on average 48 varmint or deer rifles, as scopes grew heavier and cartridges more powerful, many shooters switched to stouter mounts without windage adjustments—and soon discovered their highmagnification scopes didn’t always line up with their rifle’s bore. Most blamed the problem on barrels not being screwed in straight, or bad mounts. Both are possible, but in reality the big problem is usually the surface of the receiver being imperfectly polished, resulting in slightly tilted scope rings. On a typical centerfire rifle, a scope’s rings sit 3 to 6 inches apart. A difference in alignment of 0.01 inch (the thickness of a thin business card) shifts point of impact 6 inches with a 6-inch spacing, and 12 inches with a 3-inch ring spacing. Over the years I’ve often seen factory rifles with 2 or 3 feet of scope misalignment at 100 yards. While your scope might adjust enough to cover 2 to 3 feet of misalignment, its adjustments won’t work the way they’re designed. The point-of-impact of internally adjusted scopes is changed by turning screws that push on the erector tube inside the scope. (The tops of the screws are the dials on the adjustment turrets.) If the A scope is mounted off-center, the screws will be off-center on the erector tube, making adjustments erratic. Also, if you’re one of those 21st-century shooters who click the elevation adjustment up and down when shooting at different ranges, there may not be the amount of “up” desired. For scope adjustments to work correctly and reliably, we need to mount the scope so the centered reticle is lined up with the bore. The reticle can be centered either optically or mechanically. For optical centering, press the front bell of the scope against a mirror, and then look through the scope as if shooting. You’ll see the reticle and its reflection, and 99 percent of the time they won’t line up with each other. If we adjust the scope so both reticles come together, theoretically the reticle will be centered in the scope. Notice the “theoretically.” Not all scopes are perfectly machined. The objective bell may not be precisely square, or the reticle itself may be off-center inside the scope. Since the purpose of centering the reticle is having the most adjustment possible, I prefer the mechanical method of twisting each adjustment dial from one end of its range to the other, counting the number of twists, then turning the dial back half that number. Once the reticle’s centered, we can mount the scope so it lines up with the bore. Traditional bore sighting will work, but only if we can look through the bore from the rear, an impossibility with semi-auto, pump and leveraction rifles, and also requires at least 20 yards of space in front of the muzzle. Far easier B C D E W W W. G U N S M AG A Z I N E . C O M • J U N E 2 0 1 3

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