Dialing for elevation requires a properly mounted and leveled scope in order to achieve accurate corrections to point of impact. (Photo courtesy of Leupold)
May 24, 2022
By Richard Mann
Modern riflescopes are optical marvels. You can haul your rifle around on an ATV and the scope will never shift zero. You can dial in bullet corrections as small as an inch at 400 yards. With zoom ranges as high as eight times, you can view a crystal-clear image at 3X to 24X. A riflescope is one of the primary interfaces between a hunter and a rifle, and we must take some steps to avoid common mistakes and optimize that interface.
The first and most critical task is mounting the scope to the rifle.
Too often hunters skimp on scope mounts only to discover the cheap mounts are the reason the setup won’t hold zero or shoot itty-bitty groups. Worse yet, cheap mounts that don’t fit the scope or rifle correctly can damage both. Precisely machined bases and rings are key to taking full advantage of a scope’s benefits.
Mount the scope as low as possible. This makes it easier to establish a good cheek weld on the stock while comfortably looking through the riflescope. At the same time, make sure at least 1/8 inch of clearance exists between the objective housing and the barrel, and the bolt handle does not interfere with the magnification adjustment.
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Eye relief, the distance from your pupil to the ocular lens in the scope, is another aspect of shooter interface. The scope should be mounted far enough to the rear so that when you shoulder the rifle from any position and comfortably rest your cheek on the comb, you can see the full field of view through the riflescope. Rubbernecking around trying to obtain a full view is detrimental to fast and good shooting.
Once you have positioned the scope correctly, make sure it is level. If the scope is not level, any adjustments you make will not move the reticle in a true horizontal or vertical direction. Leveling a riflescope can be tricky, but there are a variety of tools available from brands such as Real Avid and Wheeler Engineering to help with the process.
Confirm the scope is level by shooting a three-shot group on a target at 100 yards, adjusting the elevation 48 clicks (1/4 MOA clicks) up and firing another three-shot group while aiming at the same spot on the target. The center of the second three-shot group should be directly above the center of the first group by about 12 inches. If the second group is left or right of the first, the scope is not level, and any elevation adjustments you make will cause the bullet to impact farther off the target at greater distances.
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Zeroing a riflescope is the first step in refining how you use it. The process is nothing more than adjusting the reticle so that its primary aiming point—where the horizontal and vertical crosswires intersect—matches the point of impact at your preferred range. Many modern riflescopes come with reticles that offer additional aiming points for extended ranges. Others have rotating turrets designed to let you dial in corrections at longer distances. With both types of scopes, a 100-yard zero is common. If your riflescope is the more traditional type and has a simple duplex reticle with capped turrets, many hunters opt for what is known as a maximum point-blank zero (MPBZ).
With an MPBZ you adjust the reticle to coincide with a point of aim that will allow you to hold dead-on a big-game animal from the muzzle out to the farthest practical distance. There are a variety of ways to do this. I use a ballistics app to determine how far my bullet will travel in 1/3 second (250 to 300 yards for most modern big-game cartridges), and then adjust the reticle so that my bullets strike 3 inches below my point of aim at that distance. The result is a zero where the bullet will never be more than 3 inches above or below my point of aim out to that range. (Also read Shooting Tips: The 1/3-Second Zero )
If you’re using turrets to dial in trajectory corrections, the MPBZ is still not a bad idea. Instead of walking around with your elevation turret set to a 100-yard zero, adjust it for an MPBZ. This way if you must make a quick shot inside the MPBZ range, you’ll not have to take time to dial in a correction. The concept can also be used with ballistic reticles that have additional aiming points. It requires some math and time on the range, but by adjusting the primary aiming point for an MPBZ, the additional aiming points will work at greater distances. Use the primary aiming point unless the target is beyond the MPBZ range.
Despite the popularity of fancy reticles and dialing turrets, some hunters prefer simpler riflescopes. You can use a common duplex reticle to adjust for trajectory and to make range estimations. Again, some math and time on the range are required. Determine the height covered by the distance from the crosswire intersection to the tapered point on the bottom vertical wire at 100 yards. Once established, you can use the tip of the taper as an additional aiming point, controlling the correction it provides by adjusting the magnification. For this technique to work, your scope reticle must be in the second
focal plane so that the size of the reticle in relation to the target changes as the magnification is adjusted.
For example, if that space equals, or subtends, 3 inches at 100 yards with the scope set at 9X, it will equal 12 inches at 400 yards at the same magnification. Similarly, it will subtend 4 1/2 inches at 100 yards and 18 inches at 400 yards with the scope set at 6X. In the same manner, you can use the tapered points on the horizontal wire for wind corrections.
These are just a handful of ways you can get the most from your riflescope. But for any of these techniques to work properly, you’ll need a scope that has been solidly mounted and that is perfectly level. Take the time to make sure that’s done correctly, and then spend some more time on the range learning to work with the precision marvel that the riflescope has become.
Subtension Calculation Use a simple duplex reticle for holdover.
The amount of space between the crosswire intersection and the tapered point on the bottom vertical wire of a duplex reticle can be employed as a reference for holdover. Start by determining this space at 100 yards by viewing a target with a 1-inch grid, and then apply the following formulas.
Range Change (NR/OR) x OS = NS NR is New Range; OR is Old Range; OS is Old Subtension; NS is New Subtension Example : If the subtension at 100 yards is 3 inches and you want to know the subtension at 350 yards, the calculation would be (350/100) x 3 = 10.5. Magnification must remain the same.Magnification Change (OM/NM) x OS = NS OM is Old Magnification; NM is New Magnification; OS is Old Subtension; NS is New Subtension Example : If the subtension at 100 yards is 2 inches at 12X and you want to know the subtension at the same range at 6X, the calculation would be (12/6) x 2 = 4. Reticle must be in the second focal plane.
