We often receive questions or hear interesting theories as to the appropriate zero for the AR-15 platform. As a result, we have compiled our reasoning for why we advocate the 50- or 100-yard zero for the platform and advise against the 25 yard zero. When asked, which is the best zero, to steal from Kyle Lamb in Green Eyes, Black Rifle, our answer is: whichever zero for which you know all your hold-offs for, or that don’t require math to figure on the fly. We also need to be more realistic about what type of shooting and at what distance we are likely to use our rifle for. So before we touch on those points, let’s look at trajectories for the various zeros a little closer.
First, we need to understand what is happening when we zero a rifle. Bullet trajectory follows the following path when it leaves the rifle:
Contrary to popular belief, gravity begins working on the bullet the second it leaves the gun. Therefore, we change the arc the round travels by changing the relationship between our front and rear sights. The relationship between the two determines where the round will strike a target at a given distance. For all zeros except the 100 yard zero, a near-zero and far-zero will be produced as the bullet passes the line of sight towards the apogee, and then drops once again through the line of sight.
Let’s examine the 25 meter zero with XM193 and a 16 inch barrel:
This zero produces a point of aim, point of impact at 25 meters, and again at approximately 382 yards. This trajectory “peaks” at approximately 200 meters, about 9 inches HIGH from the point of aim.
Now the 50 yard zero, also referred to as the Santos Improved Battlesight Zero:
This zero produces a point of aim, point of impact at 50 yards, and then again at approximately 225 yards. This zero only produces a “peak” about 2 inches high at between 125 and 150 yards.
Finally, the 100 yard zero:
As you can see, with this zero, the round “kisses” the line of sight at 100 yards, and then travels back below, and only has one point of aim, point of impact, unlike the other zeros shown.
Because the y-axis scale on the other charts can be misleading and give the illusion that the 25 meter and 50 yard zeros have less arc, here is all three zeros together on the same graph.
Now let’s look at bullet drop in inches for the different zeros in chart form.
|Range (yards)||25 YD Zero||50 YD Zero||100 YD Zero||200 YD Zero|
Source: Green Eyes, Black Rifle, Kyle Lamb, Viking Tactics, Inc. 2005
As is evident by the chart, the 25/374 yard zero has quite a bit of slope to it and requires accurate range estimation and memorization of hold-over or hold-under at many distances, where as the 50/210 yard and 100 yard zero are generally within 2 inches of each other out to 200 yards, requiring far less precision in range estimation of recall of corresponding hold-over or hold-under.
Next, ask yourself at what distances you are most likely to shoot your rifle? If it’s a home defense weapon, I think you would be VERY hard pressed to conceive of a situation where you would be shooting past 50 yards, and even that is pushing it. Even for the law enforcement officer, it would be hard to think of a situation in which you would be engaging targets past 100 yards, unless you are a designated marksman on a roof with a spotter and a bolt action rifle. The only exception may the infantry rifleman, who may engage targets near and far. But even for the military rifleman, many engagements in our current theater of operations are happening in a MOUT environment at CQB distances. As you can see from the chart above, out to 200 yards with a 50 or 100 yard zero, rounds will impact within two inches of point of aim, so even if you forgot to compensate in the heat of battle, you would still produce accurate, effective shots that would adhere to the accuracy standards set by many of today’s top-tier instructors of hand-sized groups.
We at Aesir Training recommend a 50 or 100 yard zero, which simplifies hold off calculation, and lessens the need for precise range estimation. However, we do not force students to zero their rifles to our exact requirements as long as students have sound reasoning for the zero they run and understand the affects that zero will have on their shooting in various circumstances. All zeros have their positives and drawbacks, but it is our opinion that the 50 and 100 yard zero offer the best of multiple worlds.
Safe shooting, we’ll see you at the range.