Texas Dept. of Defense

Texas Dept. Of Conservation
September 25, 2017
TEXAS HOT SHOTS
September 25, 2017

Scopes and Ballistics

H itting a target at long-range with a scoped rifle ain’t easy.

Doping wind, estimating range, and compensating for bullet drop present a mind-boggling mix of skills that few shooters have the time or dedication to master.

However, “experts” (who eagerly bestow “knowledge” on the rest of you poor unenlightened souls) abound on the internet. I am one of those experts, but I own the sole distinction of being correct in all things. So, ignore the others.

How do you know what I say is true? It HAS to be true—you saw it on the internet.

Now that we’ve settled that, it’s time to dispel a few myths and misconceptions about riflescopes, bullet trajectories and such—some of which have lingered for many decades.

One comes to mind that I often heard back in the ’50s and ’60s: “When a bullet leaves the muzzle, it rises for a while before it begins to drop.” Whenever I saw this in print, some genius would debunk this as a myth. They’d point out that gravity makes a bullet begin to drop immediately the instant it leaves the muzzle and imply that whoever thought differently was simply ignorant.

Well, yes. Gravity DOES work that way—it’s just irrelevant to the matter at hand. Here’s why:

As you look through your riflescope, the crosshair intersection represents the center of your line of sight, which extends straight as a string all the way to your target. If your eye and the target are at the same elevation, that line of sight is perfectly horizontal.

For a typical riflescope, your line of sight lies 1.5 inches (more or less) above the centerline of your rifle’s bore, which the bullet passes through en route to that target. If your rifle is properly zeroed (or sighted-in)—at, say, 100 yards—the path of the bullet must intersect your line of sight at that distance. To do this, the rifle’s bore must TILT UPWARD slightly to launch the bullet on an UPWARD path in order to intersect your line of sight.

Guess what—When the bullet leaves the muzzle, it DOES rise for a while before it begins to drop.

We can’t blame this little gem on the internet because back in the ’50s and ’60s, it didn’t exist. Armchair experts DID exist in those days, though. Many of them were gun writers who stated “facts” that often weren’t true—just like today’s internet experts.

Also dating back to that era, is a sighting-in method designed to take advantage of a rifle/cartridge’s long-range capabilities. This one is not really a myth or misconception. It’s just—in my humble opinion (IMHO)—a poor way to use your rifle’s trajectory.

In recent years, this has been touted as the “Maximum Point-Blank Range” method. (Let’s call it MPBR.) It takes advantage of the relatively flat trajectory of many high velocity cartridges such as the .270 Winchester and most magnum rifle cartridges.

Incidentally, the trajectories of this class of cartridges are very similar, varying less than an inch or so out to nearly a thousand yards. So, MPBR works about the same for most flat-shooting cartridges.

Using MPBR, you sight-in so the bullet is three or even four inches high at 100 yards. At 150 to 200 yards the bullet will still be more than four inches high at the highest point (mid-range trajectory). Beyond 200 yards it will start arcing down to intersect the line of sight for a long-range zero of about 300 yards.

A duplex reticle can be used to
“eyeball” ballistic drop compensation.

The bullet will now begin dropping more rapidly. At 350 yards it will be about four inches low, and by 400 yards, it will drop to around 10 to 12 inches low. As it passes 500 yards, the bullet will now be about two and a half feet below your line-of sight.

Keep in mind that a deer-sized game animal standing broadside with your scope reticle centered just behind the foreleg has a heart-lung kill zone roughly 10 to 12 inches high. This MPBR zero puts your bullet within four inches above or below line of sight—that is to say, an eight-inch diameter cone of fire out to 350 yards or so. That’s well within the kill zone of deer-sized game.

Does that sound okay to you? For me—not so much.

Those who compile hunting statistics say that most rifle-killed big game are shot at less than 200 yards. What makes more sense to me is a sight-in zero designed for this kind of shot—but one that still works just fine at long range.

For the purpose of this discussion, I’ll assume a few things about your deer-sized quarry (Oh heck, let’s just say “deer”).

(1) Beyond 200 yards, the deer is probably not alarmed and might not even be aware of your presence. If so, you probably have plenty of time to plan and take an unhurried shot.

(2) Nearer than 200 yards, the odds that a deer will see or smell you increase considerably. If the deer is closer than 100 yards, the odds go way up. If so, the deer might be ready to “get out of Dodge,” giving you only seconds to shoot.

(3) Deer, especially whitetails, like brushy and wooded areas. So, you might have to shoot past limbs that could deflect your bullet.

Some or all of the above conditions might not occur all, or even most of the time, but why not be prepared? If you need to aim quickly and/or shoot past intervening brush, a four-inch gap between your bullet’s flight and your line of sight is just asking for trouble.

Here’s a better solution—sight-in your rifle only ONE inch high at 100 yards. This zero keeps even medium-powered cartridges, such as .308 Winchester and .30-06 within an inch above or below line of sight slightly past 200 yards.

Flat-shooting rounds from .25-06 to .30 caliber magnums will have a similar trajectory, but a few tenths of an inch flatter. If you’ve sighted-in this way, you merely put your crosshair where you want to hit and quickly take the shot.

Assured that your bullet will hit within an inch of where you aim, you can be confident of a humane, quick kill. Also, with your bullet’s flight hugging tight to your line of sight, you minimize the chance of an unnoticed tree limb deflecting your bullet.

Beyond 200 yards, a “ballistics reticle” or even a thick-thin crosshair similar to Leupold’s Duplex reticle will give you a good long-range aiming point. In next month’s column, I will go into more detail on how a ballistics reticle is a valuable aid to accurate long-range shooting.

—by Stan Skinner

Poor Man’s BDC Reticle

The world of shooting optics is massive with seemingly infinite options. MIL or MOA adjustments? First focal plane or second? Fixed, side turret or bell parallax adjustment? MIL-Dot, Horris, or MOA reticle? Nightforce, Leupold, Meopta, Bushnell or countless other manufacturers? But with this technique you can keep it simple and use any duplex reticle as a poor man’s Ballistic Drop Compensation (BDC) reticle. 

Duplex reticles can be used for double zeros for fixed distances. For instance, we use the Marksmanship Camp’s Volquartsen Custom .22LRs mostly at 50 yards for the kids. However, I enjoy shooting from 100 yards. So, I don’t adjust zero on the turrets every time I move back and forth.

Instead, I adjust the magnification on the second focal plane reticle so the lower duplex point is exactly where my 100 yard shot will land. The easiest way to do this is to fire a shot on a clean target from the distance in question. Then adjust the magnification until the point of the lower duplex rests on the point of impact while your crosshairs hold on the original point of aim.

I was lucky enough that it matched right on the point of the “7” on my Meopta scope so it’s very easy to replicate. You might have to put a small scratch or use a fine-tipped marker noting the exact magnification setting to be able to adjust back and forth.

This will only work with variable magnification second focal plane optics because the reticle will not change size with the magnification. 

The most common range finding and BDC scope reticle is the mil-dot so we can also use that as a target objective for the remainder of this tutorial, however this technique could be adapted to any other measurement as well.

A “mil” relates to the US military variation of a unit of angle known as a milliradian. The distance between the centers of any two adjacent dots on a mil-dot reticle is one mil, which is 36 inches at 1,000 yards, or 3.6 inches at 100 yards.

With this constant we can range distance of targets if we know their size, and use the mils as point of reference for holds for ballistic drop.

However, what if you don’t have a fancy mil-dot scope, just a cheapo Tasco with a duplex reticle? If that Tasco holds zero and shoots straight, you can find what magnification the duplexes match a mil measurement and use the same formulas for long range shooting.

Begin by marking 3.6 inches (3 5/8 inches) or downloading a mil target and set it at 100 yards. Then find a stable position to determine at what magnification setting you can fit a mil between the center of the crosshairs and a point of the duplex.

From here you can use the standard formulas for ranging: size of the object in yards x 1,000 divided by size of the object observed in mils = range in yards. Then you could also use it for hold over.

For instance if your target is 300 yards away, and your .308 drops 13 inches, then 13 inches at 300 yards would be 1.2 mils. Give the appropriate elevation hold below the first duplex estimating 1.2 mils and you should be right on the mark.

Is this practice ideal? No, it can be a bit complicated and not as accurate. But it will work in a pinch and is a great way to expand your training toolbox in being intimate with your rifle system.

—by Dustin Ellermann

 

 

Email Steve LaMascus at [email protected]

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