September 23, 2010
By John Antanies
Six pieces of gear that will help you connect at big yardage.
By John Antanies
Anyone who has ever read a word David Tubb has written knows that attention to detail is a key to becoming a successful long-range rifleman. Some of these details are mastered only through years of experience, but there are other small details that can be mastered by simply spending a few bucks. And there is no better area to start than your long-range scope.
The first challenge for long-range shooters is simple: The farther the range, the more the bullet drops. Meeting this challenge requires two things: the ability to determine the range and some method to allow for the bullet drop.
Determining the range today is about as simple as buying a good rangefinder and then testing it to identify its limitations. Compensating for trajectory is a bit more complicated but made dramatically easier for reasonable hunting ranges with the introduction of ballistic reticles--reticles with multiple aiming points for targets at 300, 400 and 500 yards, etc.
But when ranges exceed 500 yards, using a simple ballistic reticle gets complicated. Most don't have any hash marks or aiming points past 500 yards, and even if they did, at this point most bullets are dropping around one inch for every five yards of travel. That means holdover lines every 50 yards just are not going to deliver the bacon.
This also illustrates another key accessory for the long-range scope: target turrets. Unless you have a ballistic reticle and limit shooting to less than 500 yards, with few exceptions you really need target turrets.
The Horus Vision is one of these exceptions. The H25 reticle is a grid system with hash marks as close as .2 mils--meaning that a hold in between the lines will allow a shooter to hold within .1 mils or .36 inches at 100 yards--almost as precise as quarter-minute scope adjustments. I have one of these mounted on a .300 Remington Ultra Mag and find it the only reticle that can compete with clicking windage and elevation.
Many scopes these days feature finger-adjustable windage and elevation adjustments. These are certainly an improvement, but these lack rotation counters--an index that counts how many full revolutions you have turned the knobs. Without rotation counters, you can spin them more than one full revolution and then forget to spin them back. If you do use target turrets, be sure to put a witness mark on the rotation line that marks your zero so that you can return to zero with confidence.
Spinning target knobs for elevation as opposed for holding over has one more advantage: You can hold on the target for elevation but hold off for windage. You can certainly dial in windage as well, but holding off for wind is quicker than dialing and avoids the error of dialing in windage the wrong way.
I go back and forth on whether holding off or dialing in wind is better, but once the wind exceeds about 7 mph at ranges in excess of 600 yards, it is pretty difficult to hold off.
While I don't shoot game at these ranges, I do practice at such distances. Like a baseball player in the on-deck circle swinging a heavier-than-normal bat, practicing at very long range makes a 400-yard shot seem like it is served up on a platter.
Shooters who want target turrets can often get them installed on standard scopes. I have had the Leupold Custom Shop add them for me. You can also get aftermarket turrets that show the range on the knob itself. Kenton Industries supplies such turret caps.
Horus Vision makes ballistic software that is easily loaded into a PDA. By inputting data for your rifle, you can get quick field trajectories — including adjustments for steep angles.
Running out of elevation adjustment on a long-range scope can sometimes be a problem, especially if the scope used has limited elevation range. Shooters faced with this problem can buy a scope base machined so that the bullet strikes 20 inches higher at 100 yards than a conventional base. Manufacturers such as Nightforce and Leupold offer such bases.
When shooting at long range, even the best rifle and scope are of little help if the rifle is canted. Canting a rifle--when the vertical crosshair is not perpendicular to the earth's surface--at normal hunting ranges (which I define as 250 yards or less) is normally no big deal. But at long range, canting your rifle can cause your bullet to strike slightly low and to the left or right, depending on the direction of the cant and the range to the target.
Why does canting affect a bullet's trajectory? Well, in order to overcome the effects of gravity, we zero our sights (or hold over) so that the bullet is traveling higher than the line of sight; the barrel is elevated with respect to the surface of the earth. At very long ranges, the bullet must travel quite a bit of distance above the line of sight.
When we cant the rifle, we actually "cant" the trajectory curve as well. To illustrate this, grab a yardstick and place it against a wall. Place a piece of tape on the wall at the top of the yardstick; this represents the highest point in a bullet's trajectory. Now cant or tilt the yardstick left or right. What happens? The end of the yardstick moves either right or left as well as slightly down, but the amount of movement in the horizontal direction dwarfs that in the vertical.
The effects of canting are easy to see if you have a ballistics software application; simply plug in the cant angle and you can see the correction required.
For example, RCBS.Load, a software ballistics program from RCBS, allows shooters to input cant using a term called "gun rotation." The results can be surprising. For example, a .308 bullet with a ballistic coefficient of .509 at 3,000 fps will hit five inches to one side at 500 yards if the rifle is canted five degrees. That's enough to cause half of your bullets to miss a 10-inch wide vital area.
For years I have used a ScopLevel spirit level. This is a small fold-down level that mounts on the scope tube via polymer rings. When faced with a long-range shot, a shooter extends the level and aims through the scope. When properly mounted, a quick glance above the eyepiece will reveal any cant.
To mount the scope leveling device, mount it on the scope but don't fully tighten the locking screws. Then take a length of parachute cord or heavy string and tie it to a tree branch; on
the other end of the cord tie a weight such as a plumb bob or even a heavy rock.
Now back up 50 or so yards and place the rifle on a rest. Sight through the scope and place the vertical crosshair over the suspended cord. Assuming the wind is negligible, this cord is perpendicular to the earth's surface, and with the vertical crosshair lined up with the suspended cord, the rifle has zero cant. Then just rotate the device until it it's level and tighten the mounting screws.
Besides eliminating canting, going through the above exercise will ensure the scope is mounted properly and the vertical crosshair is perfectly perpendicular to the earth's surface. If it's not, your scope adjustments will not track accurately; they will drift left or right as you change elevation.
The Nightforce ADIMT indicates inclination angles. It mounts on a standard Picatinny rail and is offset so it sits just underneath and to the left of the scope tube.
Most shooters know that shooting uphill or downhill will cause the bullet to hit high. The solution to this problem is not as simple as holding for the true horizontal distance; time of flight does matter. To use an extreme, it takes a bullet longer to fly 700 yards fired uphill at a 45-degree angle than it does to travel 490 yards over flat terrain (the true horizontal distance).
Before the days of laser rangefinders, a long shot was 400 yards. At that range, simply holding about five inches low on a steep incline or decline works well (assuming you have a flat-shooting cartridge). I once shot a sheep at an estimated 360 yards using just this trick. But today there are better tools that make long-range shooting at inclines easier.
Nightforce Optics makes an instrument that measures the angle of incline/decline. It is called the ADIMT, and it mounts on a Picatinny rail and displays a rifle's deflection angle using a small dial. I mounted one on a .300 Remington Ultra Mag, and it works wonders.
Techno types can take this a step further and pair an angle indicator with a PDA loaded with ballistic software. Horus Vision ATrag software is easily loaded into a PDA, and Sierra offers its Infinity program for Windows-based PDAs.
With the ATrag, you can load any number of different cartridges, defined as "Gun Lists." All you need to know is the rifle's muzzle velocity and the bullet's ballistic coefficient.
Shooters who don't know the muzzle velocities of their cartridges can actually calculate them by zeroing at 200 yards, shooting at 300 and 400 yards, and then measuring the bullet drop at each range. Simply add or subtract from the muzzle velocity in the "Gun List" entry until the field trajectory matches that from ATrag.
If you can't afford the PDA solution, check out the Leupold Ballistic Chart--a handy drop chart that mounts on your scope.
The latest trend with rangefinders is to calculate the "true ballistic range" (see accompanying sidebar). Note they don't advertise "true horizontal distance" because there is more to uphill/downhill angles than the horizontal distance. These rangefinders use approximate rifle trajectories to provide an equivalent distance or in some cases, provide the holdover.
These rangefinders are faster than using the ADIMT/PDA solution, and they probably measure the inclination angle more accurately, but since a shooter cannot as of yet input his own ballistic data in order to tailor the unit to a specific load, they may be less precise.
The last valuable piece of gear for long-range shooters should have is a pocket wind speed gauge such as the Kestrel. Knowing the speed of the wind at your shooting site doesn't mean it is blowing the same at the target, but the wind at your site is the most important.
A pocket anemometer can also show how much the wind is varying, and a good long-range shooter will know when that creates too much uncertainty and require repositioning for a closer shot.
The best of these meters also show barometric pressure and temperature, both of which affect bullet trajectory and both of which can be accounted for in PDA ballistics software such as Horus Vision's ATrag.
There are other accessories for the long-range scope, but a custom reticle, target knobs, a leveling device, an angle indicator, a PDA with ballistic software and an anemometer provide a lot of bang for the buck. If it sounds like a lot, it is--but long-range shooting is no easy task.
Special turrets from Leupold allow shooters quick access to trajectory data, and the ScopLevel will let you know if your rifle is canted, which can significantly affect shot placement.