Take guesswork out of long-range shots
|Photo by SOC CLAY|
If you’re planning to take a long shot with your rifle, you’d better have spent a lot of time at the range. Otherwise, luck is all you can hope for.
“I have a Remington Model 700, Sendero, 7mm Mag., with a Burris 4x16 target scope, using Hornady 139-grain Custom Interbond Ballistic Bullets.
“A friend told me that somewhere in the computer world there was a site that could take the gun and bullet information and give you the adjustment information. If you have any suggestions please let me know…”
The above question was posted to the Louisiana Sportsman website, and caused a bit of head-scratching before it was referred to me.
“I’m not sure exactly what he’s asking. Maybe you can figure it out,” said the e-mail from the editor.
As nearly as we can determine, the above writer was looking for a quick and easy way to adjust his scope crosshairs with the elevation knob, estimating the distance to the target and turning the elevation knob a set number of clicks rather than utilizing “holdover” and aiming the scope a little higher on the target to compensate for bullet drop.
I hate to disappoint, but what he is asking is almost impossible to determine. He apparently wants to do something strictly by computer that has to be conducted physically on the range.
Once the particulars of the trajectory of his bullet are established, it is then easy to keep a record of what number of clicks will move a bullet’s strike by how much, and you can adjust your knobs accordingly.
You can. I wouldn’t.
There are computer programs that determine where a bullet will strike in relation to the line from muzzle to target. In other words, inputting certain basic information will tell you where the bullet will strike at various ranges above and below a line drawn directly from the muzzle to the target, and such programs are available for sale if you want to go to that amount of trouble.
Jack Milton, owner of the Baker Range (225-775-2268), a family-owned indoor shooting range, has such a program on his computer that will tell a hunter exactly where to have his bullet strike at 25 yards so that it will be dead-on point-of-aim at another distance, say 100 or 200 yards. This program will extrapolate that information all the way out past 900 yards.
With this program, a hunter can sit in the indoor range, shoot at a target at 25 yards, and know where in relation to the aiming point on the target he wants his bullet to strike to be dead on at a specific distance. And, it works.
I still prefer sighting in on a 100- or 200-yard range, but in a pinch, this is a fairly accurate way of accomplishing a quick sight-in. Generally speaking, you will sight your bullet strike below point of aim about half the space the line of sight of the scope is above the bore. This will cause the bullet to strike about dead-point-of-aim at 100 yards.
To gain this information, you have to have some pretty detailed information to give the computer. For instance, you have to know how far above the center of the bore the center of the scope is mounted. You have to know the velocity of the cartridge you are shooting, and you have to know the ballistic coefficient of the bullet you are shooting.
Unless you are shooting a scope with a 50mm objective, and it is mounted on tall posts, the average height of most scopes above the bore is 1.5 inches.
If you don’t have a chronograph readily available, you can go to almost any reloading manual, and it will give you velocities with a number of different powders and load weights. If you are shooting factory loads, many types give you the velocities on the box, or you can call the manufacturer.
The ballistic coefficient of a bullet is the index of a bullet’s ability to overcome air resistance in flight. It is figured in comparison with a standard projectile used to calculate ballistic tables. The b/c is figured from the weight and design of the bullet.
Short, fat bullets offer more wind resistance, and thus shed velocity much faster.
In layman’s terms, the ballistic coefficient of a bullet tells the rifleman how “flat” the bullet will shoot. Some bullets with a poor b/c and relatively low velocities will fly straight out of the barrel for a short ways before starting to drop rapidly.
Cartridges like the .30-30, the .35 Remington, the .444, and the .45-70 are considered to be “short-range” guns, and the ballistic tables generally show them to be sighted dead-point-of-aim at 100 yards.
More streamlined, longer bullets such as the .270, .308, .30-06, or the magnums such as the 7mm Remington and .300 Winchester Magnum have longer bullets that travel in a straighter line for much farther before they begin to fall.
Such bullets have a much higher ballistic coefficient, and thus carry flatter, farther before beginning to drop from their flight path rapidly. These types of rifles are generally shown on the ballistic tables to be sighted in dead-point-of-aim at 200 yards.
As a comparison, a 150-grain Speer bullet, .308 diameter (the actual bore size of the .30-30), with a flat soft-point bullet has a b/c of 0.268. With a muzzle velocity of 2,200 feet per second, this bullet can be sighted dead-point-of-aim at 100 yards, and it will be 8.1 inches low at 200 yards.
The same weight bullet in a streamlined spitzer-style with a pointed soft point and a boat-tail base carries a b/c of 0.423. Fired at a muzzle velocity of 2,200 fps, this bullet can be sighted in to strike dead-point-of-aim at 200 yards, and it will be 14 inches low at 300 yards. This is fairly close to a standard load for a .308 Winchester rifle.
Obviously, the higher b/c allows the bullet to fly farther, flatter, with less drop out to a certain point. However, whenever a bullet begins shedding velocity, it starts dropping like the proverbial stone, and falls in a pronounced arc at the end of its effective range.
The bullets with a low b/c will shoot relatively flat out past 100 yards, then they start dropping. Fast.
The bullets with the higher b/c will travel flat on out past 200 yards, and then start dropping fast.
The whole point of all this mental exercise, of course, is being able to effectively hit a game animal at longer distances without having to guess as to where to put the crosshairs of a scope to gain a quick, humane kill.
And thus we come back to the original question-of how many clicks to turn the elevation knob on a scope in order to put the center of the crosshairs on the animal and pull the trigger, being assured of a hit without guessing about holdover.
“Holdover” is how high to hold the crosshairs above the aiming point on the animal so the bullet “falls,” or arcs, downward into the point of aim.
I wouldn’t do this for a number of reasons. The first and foremost is that once I get that scope set, I don’t want to screw with those settings. Far too many scopes retain a sort of “memory” — the knobs turn, but the crosshairs don’t move exactly to where they have been adjusted until after the first shot, which literally jars them into place.
One gunsmith friend recommends doubling the number of clicks you need to move the knobs to adjust, and then turning half-way back. In other words, if you need to move the vertical crosshair six clicks to the left to move the bullet strike 1.5 inches to the left, he recommends moving the crosshairs 12 clicks to the left, then coming back six to the right.
I’ve tried it, and had mixed results. It seems to work better than beating on the scope rings, trying to replicate the strike of recoil to jar the scope into place, and I have some fairly high-quality glass that still “jumps” occasionally.
So we know of no computer program that will tell you how many “clicks” to adjust your scope to compensate for bullet drop, and strongly recommend against trying to adjust the scope in such a manner anyway. You’re just going to get it out of alignment.
Apparently, the writer has some pretty nice equipment — a Model 700 Sendero and a Burris target scope do not trade hands for small amounts of barter beads, so the rifle/scope combination is excellent.
Also, the Hornady Interbond is an excellent choice for a hunting bullet, and I consider 139 grains to be the optimum weight for whitetail deer to gain the most effective b/c for long-range shooting. A bullet weight of 140 grains or so generally offers a higher b/c that translates into a flat-shooting bullet that eliminates all the guesswork out to any reasonable range, and it retains plenty of striking energy even at long ranges to effectively and humanely take a deer.
My advice to this writer would be to take the trouble to go to the range and sight this combination in around 2 inches high at 100 yards. This is going to give him a dead-point-of-aim somewhere on the long side of 200 yards, and in the vicinity of 6 inches low at 300 yards.
In other words, anywhere out to 300 yards, just aim dead at where you want to hit the animal. Anything farther than that, you need to practice a little more because you’re going to see the bullet striking about 12 inches low at 350 yards, and about 20 inches low at 400 yards.
Ask me how many deer I’ve missed at 400 yards because I held right at the point of the top of the shoulder, and the bullet flew right under their brisket-until I learned to quit “holding on hair” and aimed about 6 inches above the shoulder. And that assumes you can judge the distance that accurately.
As you can see, once you get past 300 yards on most of these cartridges, they start dropping rapidly, and a miscalculation of 50 yards, easily done at these ranges, can result in another 6 or more inches of bullet drop.
Remember the “stone” theory — the drop, or arc, increases exponentially out past 300 yards on most “long-range” cartridges.
Leupold optics has designed a scope crosshair that overcomes some of this guesswork.
Shown in the accompanying diagram, it is called their “Ballistic Aiming System,” and seems to be as effective a method for estimating “holdover” as anyone has come up with yet.
As the diagram shows, sighting the scope in to a 200-yard zero allows you to use the smaller triangles below the intersection of the crosshairs to aim dead-on at longer ranges. The edges of the triangles can be used to compensate for an average 10-m.p.h. crosswind.
And all of this can be done without messing with your elevation and windage knobs, a thought that makes cold chills run down my spine. After spending interminable hours on a range getting my rifle tuned “just so,” why would I knowingly adjust the scope off the settings I worked so hard to achieve?
Now Leupold has come up with a way to physically see the aiming point rather than guessing and using “holdover.”
Of course, when all is said and done, you’d better be able to accurately judge distance to begin with, or all this is to no avail — which means you need a laser range finder, but that’s a subject for another column.
Gordon Hutchinson’s best-selling novel, The Quest and the Quarry, can be ordered at www.thequestandthequarry.com, or by calling (800) 538-4355. Orders are sent out the next business day after they are received.
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