In this past weekend’s Defensive Long Gun class, the first thing done in the class was discussion of zeroing. Students were lined up at 5 yards, 15 yards, 25 yards, and 50 yards. A white 6″ paper plate was put up, and the students were told to aim at the center of the plate. We didn’t want students to adjust their shooting, we didn’t want them to try to put the holes in the center of the plate. Aim in the same spot every time as we vary distance so one can see the effects of their zero, the effects of distance upon their zero, the effects of distance as it pertains to point-of-aim vs. point-of-impact and so on.

Remember, the point of KR Training’s Defensive Long Gun is to look at long gun use in a civilian defensive context. So what does that likely mean? Something goes bump in the middle of the night. Strictly speaking that’s not the only scenario, but it helps to frame the context for the class. This isn’t military tactics, this isn’t shooting out to 300 yards. In fact, most of the shooting inside a typical home or office isn’t going to go above 25 yards. That frames the class.

Students came to class with a wide variety of zeros. Some had the traditional hunting “zeroed at 100 yards”, some had 25 yard zeros, some had 50 yards, some … well, we don’t know. 🙂   I’ve got a cool iOS app called Ballistic, and I wanted to run a bunch of numbers through it so you could see what the effects of different zeros are.

Settings

Ballistic comes with a large library of projectile characteristics. Since most students came with AR’s chambered in .223/5.56, I picked Hornady TAP .223 Rem 75 grain HP, because that’s a reasonable choice for a home defense load. As well, I chose a sight height of 2.5″, which isn’t strictly correct but is good enough to talk some numbers. But whatever the specifics, I kept all those variables the same, only changing the zero point since that’s the intent of the discussion.

100 yard zero

A typical zero is the 100 yard zero, meaning that your point-of-aim and point-of-impact are the same at 100 yards. This is a very common zero for rifles, especially in the hunting realm.

Here’s the chart generated:

And here’s a graph of that trajectory:

300 Yard Zero

The old school military approach was a 300 meter zero. In the interest of keeping things as apples-to-apples I ran the numbers on 300 yards instead of 300 meters. So, not strictly the same, but it’s all still good enough for the point of the discussion.

Input Parameters .224 Hornady 75gr TAP HP BC Bullet Weight Muzzle Velocity Zero Range Sight Height LOS Angle  0.395 G1 75gr 2790 300 2.5 in 0° Altitude Pressure Temp RH Wind Velocity Wind Angle 705.0  30.06 Hg. 68.0 °F 56% 0.0 90° Zero Altitude Zero Pressure Zero Temp Zero RH Optimum PBR Zero 705.0  30.06 Hg. 68.0 °F 56% 291 Bullet Trajectory  Range (yards) Drop (in) Drop (moa) Wind. (in) Wind. (moa)  Veloc. (fps) Energy (ft-lbs) Time (sec)   5 -2.07 -39.44 0.00 0.00 2786 1292 0.01   10 -1.64 -15.67 0.00 0.00 2774 1282 0.01   15 -1.23 -7.82 0.00 0.00 2763 1271 0.02   20 -0.83 -3.95 0.00 0.00 2751 1260 0.02   25 -0.44 -1.67 0.00 0.00 2739 1249 0.03   30 -0.06 -0.19 0.00 0.00 2728 1239 0.03   35 0.31 0.84 0.00 0.00 2716 1228 0.04   40 0.66 1.58 0.00 0.00 2705 1218 0.04   45 1.00 2.13 0.00 0.00 2693 1208 0.05   50 1.33 2.55 0.00 0.00 2682 1197 0.05   55 1.65 2.87 0.00 0.00 2670 1187 0.06   60 1.96 3.12 0.00 0.00 2659 1177 0.07   65 2.25 3.31 0.00 0.00 2647 1167 0.07   70 2.54 3.46 0.00 0.00 2636 1157 0.08   75 2.81 3.57 0.00 0.00 2625 1147 0.08   80 3.06 3.65 0.00 0.00 2613 1137 0.09   85 3.31 3.71 0.00 0.00 2602 1127 0.09   90 3.54 3.75 0.00 0.00 2591 1118 0.10   95 3.76 3.77 0.00 0.00 2579 1108 0.11   100 3.96 3.78 0.00 0.00 2568 1098 0.11   105 4.15 3.78 0.00 0.00 2557 1089 0.12   110 4.33 3.76 0.00 0.00 2546 1079 0.12   115 4.50 3.73 0.00 0.00 2535 1070 0.13   120 4.65 3.70 0.00 0.00 2524 1061 0.14   125 4.79 3.66 0.00 0.00 2513 1051 0.14   130 4.91 3.61 0.00 0.00 2502 1042 0.15   135 5.02 3.55 0.00 0.00 2491 1033 0.15   140 5.12 3.49 0.00 0.00 2480 1024 0.16   145 5.20 3.42 0.00 0.00 2469 1015 0.17   150 5.27 3.35 0.00 0.00 2458 1006 0.17   155 5.32 3.28 0.00 0.00 2447 997 0.18   160 5.36 3.20 0.00 0.00 2436 988 0.18   165 5.39 3.12 0.00 0.00 2425 979 0.19   170 5.40 3.03 0.00 0.00 2414 971 0.20   175 5.39 2.94 0.00 0.00 2404 962 0.20   180 5.37 2.85 0.00 0.00 2393 953 0.21   185 5.34 2.75 0.00 0.00 2382 945 0.22   190 5.28 2.66 0.00 0.00 2371 936 0.22   195 5.22 2.56 0.00 0.00 2361 928 0.23   200 5.14 2.45 0.00 0.00 2350 920 0.23   205 5.04 2.35 0.00 0.00 2339 911 0.24   210 4.93 2.24 0.00 0.00 2329 903 0.25   215 4.80 2.13 0.00 0.00 2318 895 0.25   220 4.65 2.02 0.00 0.00 2308 887 0.26   225 4.49 1.91 0.00 0.00 2297 879 0.27   230 4.31 1.79 0.00 0.00 2287 871 0.27   235 4.12 1.67 0.00 0.00 2276 863 0.28   240 3.91 1.55 0.00 0.00 2266 855 0.29   245 3.68 1.43 0.00 0.00 2255 847 0.29   250 3.43 1.31 0.00 0.00 2245 839 0.30   255 3.17 1.19 0.00 0.00 2234 831 0.31   260 ↓ 2.95 1.09 0.00 0.00 2226 825 0.31   261 2.89 1.06 0.00 0.00 2224 824 0.31   265 2.59 0.93 0.00 0.00 2214 816 0.32   270 2.27 0.80 0.00 0.00 2204 808 0.33   275 1.94 0.67 0.00 0.00 2193 801 0.33   280 1.59 0.54 0.00 0.00 2183 794 0.34   285 1.22 0.41 0.00 0.00 2173 786 0.35   290 0.83 0.27 0.00 0.00 2163 779 0.35   295 0.43 0.14 0.00 0.00 2152 771 0.36   300 ↑ -0.00 -0.00 0.00 0.00 2142 764 0.37

And here’s a graph:

50 Yard Zero

The 50 yard zero is based upon the notion of the (Revised) Improved Battlesight Zero. The intent behind this zero is that when zeroed at 200 meters, the rifles have a fairly flat trajectory within about 2″ of the line of sight between 0 and 200-250 meters. That’s pretty good for  hitting man-sized targets fairly accurately under pressure. What’s a happy conincidence here is a zero at 200 meters also has a zero point at 50 yards, just due to how the bullet rises and falls in its flight path. Not everyone has access to a 200 meter rifle range, but most people can get 50 yards at a range. How handy!

And here’s the chart:

25 Yard Zero

A 25 yard zero seems right and appropriate for the context: home defense, won’t be shooting past 25 yards (as a generalized statement).

And the picture worth 1000 words:

Analysis and Discussion

That’s a lot of numbers to sort through.

Let’s first focus on the context of the discussion: the home defense situation, looking at things out to 25 yards. All of the bullets start at the same place: 2.5″ low at 0 yards. So where do they end up at 25 yards?

100 yard zero	-1.43″
300 yard zero	-0.44″
50 yard zero	-1.11″
25 yard zero	0.00″

Based upon this table, it looks like the 25 yard zero is what you’d want, right? it puts it all right where you want it with minimum concern for holdover and adjustment. If you draw a line between the height at zero yards to the height at 25 yards, the 25 yard zero “corrects” much faster and gets your point of aim closer to your point of impact.

That’s all good, right?

Well… are you sure you’re only going to have to shoot at 25 yards and no further? What if this is a person kidnapping your child and they’re running out the door… you’re running after them. Taking a shot while you’re running isn’t going to help your accuracy so you stop to steady yourself, but they’re still running, getting further and further from you. Could they be 100 yards away by the time you need to take that shot?

So what do things look like at 100 yards?

100 yard zero	0.00″
300 yard zero	3.96″
50 yard zero	1.29″
25 yard zero	5.71″

Look at those numbers. That 25 yard zero now has you nearly 6″ over your point of aim. If we say the vital area is about the size of a 6″ paper plate, you’ve well missed (assuming you’re aiming for the middle of the vitals, so you’ve only 3″ above that point to work with)… or can you calculate the holdover (under) that you need to adjust for under that sort of time and life pressure? Of course, now that you’ve missed, you’ve actually made an unacceptable hit.

Even the 300 yard zero goes over the edge of acceptable.

We’re left with 100 yards and 50 yards.

100 yard zero isn’t bad, but 50 yard zero? That gives you about 50 more yards of range. The intent is you just put your red dot or your crosshairs on the point you wish to shoot, and you’ll get within 3″ of that point of aim… maybe 3″ high, maybe 3″ low, but it’s good enough. No need to calculate and estimate holdover, just point and click.

Of course, you still need to know your holdovers, but you can find ways to rough them. For instance, at the close “home defense” ranges, just aim higher, e.g. aim for the forehead.

For me, I like the theory of the 50 yard “battlesight zero”. It takes advantage of the ballistics of the round to give a fairly flat trajectory and thus about as wide a range as possible over which you can shoot and get your hits within an acceptable area. When you don’t have time to do precise calculations and just have to rough it, it gives you something faster to work with. It’s the trade-off. But that’s what I use on my home defense carbine. For my hunting rifle? I zero it 1″ high at 100 yards. There is no one zeroing solution because it depends upon the equipment (the gun, the scope, the height of the scope over the bore, the ammunition), and upon the context (hunting, home defense, etc.). Even within context, it depends upon YOUR context. Home defense for me in my city home is rather different from home defense for someone living in the country that might have 200 yards to the fence line and actively uses their rifle to deal not just with potential 2-legged predators, but regularly contends with the 4-legged ones (coyotes, feral hogs, etc.).

What’s important is to not rely upon some sort of tradition, dogma, or the way my grandpappy always did it. Or even what some guy on the Internet tells you. 🙂  It’s important to understand your situation, your needs, your equipment, your capabilities, and determine the solution that works right for you. Don’t be afraid to experiment to help you determine that solution and come to a better and well-reasoned solution. Understand then the strengths and limitations of that solution. Proceed accordingly.