Some Thoughts On Zeroing The AR-15/M16/M4 Rifles.

The current US Military doctrine is to zero at 250 meters (273 yards) which equates to a 25 yard point of impact of .9" low or dead on at 40 yards with the full size M16 and M855 ball ammo.  For the same 250 meter zero for the 14.5 " M4 the 25 yard point of impact is .7" low at 25 yards or dead on at 36 yards.  Some organizations and instructors like other zeroing techniques such as a 25 yard or 50 yard point of impact.  In an effort to see what these zeroing strategies actually do below are the results from numerous runs with ShootingLab using actual recorded velocities from an M4 and  the Aberdeen Proving Ground supplied G7 ballistic coefficient of  .151.  Note that the nominal sight height is 2.5".  Note the very high mid-range trajectory of the "25 yd zero."

My personal zeroing philosophy is to set the far zero based on a chosen size of a "vital zone."  I usually use a 6" diameter vital zone which means that the maximum ordinate is not more than 3" and the "point blank range occurs where the bullets path is 3" below the line of sight. 

M4 Carbine (14.5") M855 Ball @ 2970fs

GI 250 meter Zero
(273 yd far zero/37 yd near zero)

25 Yd Zero
(370 yd far zero)

50 Yd Zero
(209 yd far zero)

6" Vital Zone Zero
(250 yd far zero/~40 yd near zero))

Range
Yards

Path
Inches

Path
Inches

Path
Inches

Path
Inches

0

-2.5

-2.5

-2.5

-2.5

25

-0.7

0.0

-1.1

-0.9

50

0.8

2.2

0.0

0.5

75

2.0

4.2

0.8

1.6

100

2.9

5.9

1.4

2.4

125

3.6

7.3

1.7

2.8

150

3.9

8.3

1.6

3.0

175

3.9

9.0

1.2

2.8

200

3.5

9.3

0.4

2.3

225

2.7

9.3

-0.8

1.4

250

1.5

8.8

-2.4

0.0

275

-0.1

7.9

-4.4

-1.7

300

-2.2

6.6

-6.9

-4.0

325

-4.8

4.7

-9.8

-6.7

350

-7.9

2.4

-13.3

-10.0

375

-11.6

-0.5

-17.3

-13.8

400

-15.8

-4.1

-22.0

-18.2

425

-20.7

-8.2

-27.3

-23.2

450

-26.3

-13.1

-33.2

-28.9

475

-32.6

-18.6

-39.9

-35.4

500

-39.7

-25.0

-47.4

-42.6

525

-47.6

-32.1

-55.6

-50.6

550

-56.4

-40.2

-64.8

-59.6

575

-66.2

-49.2

-75.0

-69.5

600

-77.0

-59.3

-86.2

-80.5

TRAJECTORY CROSSES LINE OF SIGHT AT 36.7 & 273 yds. 
PATH IS 3.91 IN. OVER LINE OF SIGHT AT 160.4 yds.
TRAJECTORY CROSSES LINE OF SIGHT AT 25 & 370.7 yds. 
PATH IS 9.37 IN. OVER LINE OF SIGHT AT 210.1 yds.  Note the very high mid-range trajectory
TRAJECTORY CROSSES LINE OF SIGHT AT 50 & 209 yds. 
PATH IS 1.66 IN. OVER LINE OF SIGHT AT 132.3 yds.
POINT-BLANK RANGE= 289.8 yds.
TRAJECTORY CROSSES LINE OF SIGHT AT 40.6 & 250.4 yds. 
PATH IS 3.01 IN. OVER LINE OF SIGHT AT 150.2 yds.
red = nominal max ordinate
green = nominal far zero
blue = nominal -1 foot path.
pink = nominal -3 foot path

While many claim that the 5.56 isn't effective past about 275 - 300 yards, modern combat experience has show the need to be able to effectively engage targets past those distances, and the enhanced (MK 262) rounds have effective ranges way past the M855.  The 25 and 50 yard zeros have the advantage of using dead center hold at the given zero range and of using ranges commonly marked out but the 25 yd zero especially, has a very large maximum ordinate (9+ inches).  The other zeros require some specific distance from point of aim for the zero at 25 or 50 yards, or the use of a "non-standard" distance for a point of aim zero.  In my mind the "250 meter" zero (39.1 yard near zero) or the 6" vital zone zero 250 yard (40 yard near zero) make the best sense and give a good compromise in hitting close and distance targets with minimal fuss.  Hold COM to 300 yards and past that hold at the top of the head., but to each his own..

 

Below is some M193 data from a 16" M4.

 

“Zero” Range (Yd) M193 Ball


Range

25
(385 FZ)

27
(365 FZ)

40
(270 FZ)

50
(184 FX)

100
(100 NZ)
(120 FZ)

150
(78 NZ)

200
(57 NZ)

250
(44 NZ)

300
(35 NZ)

0

-2.5

-2.5

-2.5

-2.5

-2.5

-2.5

-2.5

-2.5

-2.5

25

0

-0.2

-0.9

-1.1

-1.5

-1.5

-1.3

-0.5

-.7

50

2.3

1.9

0.5

0.0

-0.8

-0.6

-0.2

0.3

0.9

100

6.1

5.3

2.6

1.5

0.0

0.2

1.0

2.1

3.4

150

8.7

7.7

3.5

1.9

-0.4

0.0

1.2

2.7

4.7

200

10

8.7

3.1

-1.0

.-2.0

-1.5

0.0

2.1

4.7

250

9.9

8.2

-1.3

-1.4

-5.2

-4.6

-2.6

0.0

3.2

300

8.1

6.0

-2.3

-5.5

-10

-9.3

-7.0

-3.8

0.0

400

-2.0

-4.8

-16

-20

-26

-25

-22

-18/

-13


Please email comments or questions to Fr. Frog by clicking here.


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Disclaimer

As far as I know all the information presented above is correct and I have attempted to ensure that it is. However, I am not responsible for any errors, omissions, or damages resulting from the use or misuse of this information, nor for you doing something stupid with it. (Don't you hate these disclaimers? So do I, but there are people out there who refuse to be responsible for their own actions and who will sue anybody to make a buck.)

Updated 2017-01-03