Effects of zeroing distance on trajectory (55FMJ)

EFFECT OF ZEROING DISTANCE ON BULLET TRAJECTORY: 55gr FMJ @3080fps

This post is written to illustrate the effect that the distance your rifle is zeroed at has on trajectory. Molon has already done a great job, but there were questions about some intermediate distances. I also want to thank lazyengineer for giving me the idea to write this FAQ as he pretty much went through the same exercise.

In this example, I used a 55gr Hornady FMJ at a muzzle velocity of 3080fps, AR15 sight height of 2.6" (same as iron sights and cowitnesses red dots and such). The bullet choice was merely to obtain a valid BC, and the muzzle velocity approximates M193 out of a 16" rifle.

NOTE: Before you ask about bullet X out of barrel Y and velocity of Z, be aware that the changes will be relatively minor from the example below. Ultimately, you should still confirm that your own rifle will shoot as projected. There is no substitute for doing this yourself. This guide is merely to show you what your options are so that you can choose what works best for you.

A good concept to think about is "point blank" range. This is the range at which you can shoot at a target (within the chosen parameter of variance) and not adjust your aim. For example: Let's use 5" as your degree of variance; the point-blank range of the 37.5 yard zero is approximately 325 yards. For a 2" variance and the 50 yard zero, your point blank range is 250 yards.

First is the 400 yard range trajectory:



You might be surprised to see that the bullet trajectory for the 25 yard zero rises 10+ inches above the line of aim at its apex! The bullet doesn't re-cross the line of sight until about 375 yards! A definite eye-opener for people who are using the 25m/300m zero that the Army teaches.

Zoomed in on the 200yard range:



As you can see, there's not a whole lot of difference in the intermediate zeroing distances.


And finally, the raw data in PDF form: http://www.ar15.com/media/viewFile.html?i=26756

The data is shown in 10 yard increments, but the trajectory is nearly linear within that range, so you can easily interpolate to any distance in between. For example: What is the trajectory at 25 yards with a 50 yard zero? We have -1.45" @20 yards and -0.92 @30 yards. Therefore, the 25 yard trajectory is (-1.45 + -0.92) / 2 = -1.185"

  Range    25yd  37.5yd    50yd  67.5yd    75yd   100yd   150yd   200yd   250yd   300yd Velocity
       0   -2.60   -2.60   -2.60   -2.60   -2.60   -2.60   -2.60   -2.60   -2.60   -2.60    3080
      10   -1.53   -1.86   -2.00   -2.10   -2.13   -2.16   -2.13   -2.04   -1.93   -1.79    3029
      20   -0.50   -1.15   -1.45   -1.64   -1.69   -1.76   -1.70   -1.53   -1.29   -1.01    2988
      30    0.49   -0.48   -0.92   -1.22   -1.29   -1.38   -1.29   -1.04   -0.69   -0.27    2948
      40    1.44    0.14   -0.44   -0.84   -0.93   -1.06   -0.94   -0.60   -0.14    0.42    2908
      50    2.36    0.74    0.00   -0.49   -0.61   -0.77   -0.62   -0.19    0.39    1.09    2869
      60    3.23    1.28    0.40   -0.19   -0.33   -0.53   -0.35    0.16    0.86    1.70    2830
      70    4.06    1.78    0.76    0.06   -0.10   -0.32   -0.12    0.48    1.29    2.28    2791
      80    4.84    2.24    1.06    0.27    0.09   -0.17    0.07    0.75    1.68    2.80    2752
      90    5.57    2.65    1.33    0.44    0.23   -0.06    0.21    0.98    2.02    3.28    2714
     100    6.26    3.01    1.55    0.56    0.33    0.00    0.30    1.15    2.31    3.72    2677
     110    6.90    3.33    1.71    0.62    0.37    0.02    0.34    1.28    2.56    4.10    2639
     120    7.49    3.59    1.83    0.64    0.37   -0.02    0.34    1.36    2.75    4.43    2602
     130    8.03    3.80    1.90    0.61    0.31   -0.11    0.28    1.38    2.89    4.72    2566
     140    8.51    3.97    1.91    0.53    0.21   -0.25    0.17    1.36    2.99    4.95    2529
     150    8.94    4.07    1.87    0.38    0.04   -0.44    0.00    1.28    3.02    5.13    2493
     160    9.31    4.11    1.77    0.18   -0.18   -0.70   -0.23    1.14    2.99    5.24    2458
     170    9.63    4.11    1.61   -0.07   -0.46   -1.01   -0.50    0.94    2.92    5.30    2422
     180    9.89    4.04    1.40   -0.38   -0.79   -1.38   -0.84    0.69    2.78    5.31    2387
     190   10.08    3.91    1.13   -0.76   -1.19   -1.81   -1.24    0.38    2.58    5.25    2353
     200   10.21    3.72    0.78   -1.20   -1.66   -2.30   -1.71    0.00    2.32    5.12    2318
     210   10.28    3.46    0.38   -1.70   -2.18   -2.86   -2.24   -0.45    1.99    4.94    2284
     220   10.29    3.14   -0.08   -2.26   -2.77   -3.48   -2.82   -0.95    1.60    4.69    2251
     230   10.22    2.75   -0.63   -2.90   -3.43   -4.18   -3.49   -1.53    1.14    4.36    2217
     240   10.09    2.29   -1.23   -3.61   -4.16   -4.93   -4.22   -2.17    0.61    3.98    2184
     250    9.87    1.75   -1.91   -4.39   -4.96   -5.77   -5.03   -2.90    0.00    3.51    2151
     260    9.58    1.14   -2.68   -5.25   -5.85   -6.69   -5.92   -3.70   -0.68    2.97    2118
     270    9.22    0.45   -3.51   -6.18   -6.80   -7.68   -6.87   -4.57   -1.44    2.35    2085
     280    8.78   -0.32   -4.42   -7.20   -7.84   -8.74   -7.91   -5.53   -2.28    1.65    2053
     290    8.25   -1.17   -5.43   -8.30   -8.96   -9.90   -9.04   -6.57   -3.20    0.87    2021
     300    7.63   -2.11   -6.51   -9.48  -10.17  -11.14  -10.25   -7.69   -4.21    0.00    1989
     310    6.93   -3.14   -7.68  -10.75  -11.46  -12.47  -11.55   -8.90   -5.31   -0.96    1958
     320    6.14   -4.25   -8.95  -12.12  -12.85  -13.89  -12.93  -10.21   -6.49   -2.00    1927
     330    5.26   -5.46  -10.30  -13.57  -14.32  -15.39  -14.41  -11.60   -7.77   -3.14    1896
     340    4.28   -6.76  -11.75  -15.12  -15.90  -17.00  -15.99  -13.09   -9.15   -4.37    1866
     350    3.20   -8.17  -13.31  -16.77  -17.57  -18.71  -17.67  -14.68  -10.62   -5.71    1836
     360    2.00   -9.69  -14.97  -18.54  -19.36  -20.53  -19.45  -16.39  -12.21   -7.16    1806
     370    0.71  -11.30  -16.73  -20.40  -21.24  -22.44  -21.34  -18.19  -13.90   -8.70    1777
     380   -0.69  -13.03  -18.61  -22.37  -23.24  -24.47  -23.34  -20.10  -15.69  -10.36    1748
     390   -2.20  -14.87  -20.59  -24.45  -25.34  -26.61  -25.45  -22.13  -17.60  -12.13    1720
     400   -3.83  -16.82  -22.69  -26.65  -27.57  -28.87  -27.68  -24.27  -19.63  -14.01    1691
     410   -5.60  -18.91  -24.93  -28.99  -29.93  -31.25  -30.03  -26.54  -21.78  -16.03    1664
     420   -7.48  -21.12  -27.28  -31.44  -32.40  -33.76  -32.51  -28.93  -24.06  -18.17    1636
     430   -9.48  -23.44  -29.75  -34.01  -35.00  -36.39  -35.11  -31.45  -26.46  -20.42    1609
     440  -11.63  -25.92  -32.38  -36.73  -37.74  -39.17  -37.86  -34.11  -29.00  -22.83    1582
     450  -13.91  -28.53  -35.13  -39.59  -40.62  -42.07  -40.74  -36.90  -31.68  -25.36    1556
     460  -16.35  -31.28  -38.03  -42.59  -43.64  -45.13  -43.76  -39.84  -34.51  -28.05    1530
     470  -18.92  -34.18  -41.08  -45.73  -46.81  -48.33  -46.93  -42.93  -37.47  -30.88    1505
     480  -21.65  -37.24  -44.28  -49.03  -50.13  -51.69  -50.26  -46.17  -40.60  -33.86    1480
     490  -24.54  -40.45  -47.64  -52.50  -53.62  -55.21  -53.75  -49.57  -43.89  -37.01    1455
     500  -27.59  -43.83  -51.17  -56.12  -57.26  -58.88  -57.40  -53.14  -47.33  -40.32    1431