How to Compute UpDown Compensation

Keep in mind that up/down compensation is quite separate from compensation for distance, even though it similarly increases with range.

Our starting point is finding "bullet drop," which is the ballistic measurement of how many inches a bullet falls when a rifle barrel is perfectly parallel to the earth. Each cartridge

Angled up/down compensation is required for rooftop shooting, such as demonstrated here atop the Pentagon.

has its own particular bullet drop data, which we're providing for .223 and .300 Winchester Magnum in the adjacent charts—and, of course, with more elaboration for the .308 168-grain Match, which is so close ballisucally to the M118LR that we're using the same data for both. (For example, at 500 yards, these two bullets are within 1/10 of an inch when compensating for a 45-degree shot. Even at 1,000 yards and 60 degrees, there's only 1 percent compensation variance.)

To find the required compensation, take this bullet drop data and multiple it by the factors shown in the "Computing Up/Down Compensation" box at right. Note that the factor changes by 5-degree increments and maxes out at 60 degrees, which is where up/down compensation itself maxes out. Compute this: find a ,223's compensation for 45 degrees up/down, when the target distance is 400 yards; 36.3

COMPUTING UP/DOWN COMPENSATION

5 Degrees: 10 Degrees: 15 Degrees: 20 Degrees: 25 Degrees: 30 Degrees: 35 Degrees: 40 Degrees: 45 Degrees: 50 Degrees: 55 Degrees: 60 Degrees:

SOURCE: Sierra

Drop inches x .004 Drop inches x .015 Drop inches x .034 Drop inches x .060 Drop inches x .094 Drop inches x .134 Drop inches x .181 Drop inches x .235 Drop inches x .293 Drop inches x .357 Drop inches x .426 Drop inches x .500

Reloading Manual

Bullet drop 30 Degrees 45 Degrees 60 Degrees

UP/DOWN COMPENSATION

.223 69-gr. BTHP Match

UP/DOWN COMPENSATION

.223 69-gr. BTHP Match

100

200

300

400

500

600

-2.0"

-7.2"

-18.2"

-36.3"

-63.3"

-101"

0.3"

1.0"

2.4"

4.9"

8.4"

13.5"

0.5"

2.1"

5.3"

10.6"

18.5"

29.5"

1.0"

3.6"

9.1"

18.2"

31.6"

50.5"

Bullet drop 30 Degrees 45 Degrees 60 Degrees

UP/DOWN COMPENSATION

.300 Winchester Magnum 190-gr. Match

UP/DOWN COMPENSATION

.300 Winchester Magnum 190-gr. Match

100

200

300

400

500

600

1000

-2.2"

-9.3"

-21.9"

-40.5"

-67.0"

-102"

-347"

0.2"

1.2"

2.9"

5.5"

9.0"

13.6"

46.5"

0.6"

2.7"

6.4"

12.0"

19.7"

29.7"

102"

1.0"

4.6"

11.0"

20.5"

33.6"

51.0"

174"

bullet drop inchcs x .293 = 10.63 inches that you must hold Ioîv to hit perfectly.

We computed the data for the three most general up/down angles of 30, 45, and 60 degrees for each cartridge just so you could get a better feel for the effect and as a reference we'll use shortJy to show how to compensate. But let's try one more example first: find the required compensation for a .223, when the target is 50 degrees up/down at a range of 500 yards.

You multiply 63.3 bullet drop inches x .357 = 22.5 inches of low hold. (Remember: always compensate by aiming low.)

Since the .308 Federal Match 168-grain BTHP is of great interest to us, we computed all this compensation data for you. By reviewing it, some points should leap off the paper at you.

First, see how we shaded it to highlight compensation of 4 inches or more. It's starkly apparent how compensation grows with the steepness of angle and distance to the target.

Second, note how significant this compensation may be even at moderate distances and gentle slopes. For example, a 20-degree slope demands 5 inches' compensation at 500 yards;

that's a lot on top of any compensation you're already taking for wind, range, and target movement.

Third, appreciate how significant the differences are for an angle of 30 degrees versus 45 degrees: think about how easy it is to snap-think a slope is 45 degrees when it's actually much less. Hold your arm up at a 45-degree angle—make sure it's really 45 degrees—and register how truly steep that is. When you're in mountains or an urban area, similarly use your arm while estimating angles to keep your conclusions accurate.

And last, while operating in urban areas, keep in mind how quickly angles increase as a hostile's position gets higher above ground. By the time he's four to five stories or higher and you're across an average downtown street, he's probably already 40 degrees up. Recall the Texas tower gunman, Charles Whitman, whose 28-story perch must have been about 50 degrees up from most lawmen, who typically fired from cover 300 yards away. This means their uncompensated shots probably hit about 10 inches high!

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