If you had to rely on one zero, what would it be?
For a long time, the mantra has been that the 50 / 200 yard zero is the most useful zero for the AR15 platform as it offers a flat trajectory for the 5.56 cartridge. It is good advice and I have a few rifles zero’ed for 50 myself, but it’s not the “best zero”. The 50 yard zero is a vanilla standard, as it suits almost everyone well… but each rifle or carbine is a unique combination of barrel length / velocity, bullet weight, and shooter. If each rifle setup is unique, then can we do better than a “vanilla” zero for each rig? Yes.
What’s the Best Zero for my AR15?
Many of you might have heard of the maximum point-blank range method of zeroing. MPBR is a zero scheme that is unique to your rifle and loading. It maximizes the “point-blank range” where you have to remember a single hold to get hits out to the end of the point-blank range, hence “maximum point-blank range.” As an example, imagine a disk six inches in diameter and I want to hit that disk as far out as possible with one zero. How would I do that? I would zero the rifle so that the trajectory of my bullet will arch 3 inches high and where the bullet would fall 3 inches below my line of sight, that would mark the end of my MPBR zero. That disk could be at 25, 100, 212, or 274.5 yards and a single-center hold would allow me to hit it with no need for holdover.
Hunters have used this method for a while, but with the popularity of the bullet drop reticle, it has fallen by the wayside in recent years. So why not just use the bullet drop marks? Because time. Your target, be it defensive or hunting, will present you with an opportune shot for only a few seconds. Ranging and doping the target, even with a BDC reticle, may not happen fast enough and / or you may miscalculate. That 18 inch shoulder-width ACOG ranging system isn’t so useful if the target is standing sideways or presents only for a split second. We want to put rounds on target, with the highest probability to intersect the target, without having to try and estimate range. Anything inside of my MPBR I want to aim at and hit without worrying about holdover, hold under, or BDC stadia. That’s the beauty of the MPBR method, it allows you to tune your trajectory to tailor suit your rifle, your loading, and your target diameter. So how do we zero with this wunder method?
Let’s start by expanding upon why we want to ditch the 50/200 zero mantra and see how things go with a 3 inch diameter MPBR:
Point. Click. Hit.
You need a ballistic calculator and some load data. I recommend Strelok on the itunes or android store. Strelok has a wonderful tool built in that lets you calculate the maximum point blank range right in the app and is a powerful tool. Let’s proceed with some more examples as to why MPBR is worth the trouble over a standard 50 yard zero.
With a 50 yard zero in a 20-inch rifle, shooting XM193, you can expect a bullet apex (aka maximum ordinate) of flight to be close to 2 inches (by my calculations) and then it falls back to cross your line of sight again at 225 yards. Wait, it’s not over yet. As the bullet continues to fall, it will fall 2 inches below your line of sight at 259 yards. The maximum point blank zero here is 259 yards meaning you should be able to hit a 4-inch disk from 0-259 yards with a dead-center hold. Think of the MPBR as the acceptable vertical resolution where the bullet’s trajectory stays inside the defined size of the target.
Now let’s bring it out a new MPBR zero which allows us to stretch that useful range out a bit more. Let’s zero so the maximum ordinate of our XM193 is 3 inches above the line of sight.
So if I am shooting a 20 inch AR15 with XM193 and a maximum bullet rise of 3 inches over my line of sight, then I just extended my MPBR to 300 yards where at that point the bullet would dip 3 inches below the line of sight. That has effectively changed our “resolution” to 6 inches where the bullet would stay in the defined target zone. A 6 inch resolution easily fits in the space occupied by a human head out to 300 yards! That means a dead hold to the middle of the face will *potentially* score head-shots out to darn near 300 yards!
Remember, this sighting method is target size defined and shooter-rifle-projectile unique. Each rifle and loading will need to be entered in Strelok (or another ballistic calculator) to determine the best zero for your desired target diameter. Why does this apply to a defensive rifle/carbine? In a self-defense setup, we need to maximize the distance where we will hit our target *without* shot correction.
If the target is inside our point-blank range… we want the rifle to be a simple “point and click” interface. Bam. Hit. We want the highest probability of hitting a head, torso, or half exposed limb. Point. Click. Hit. We want to maximize bullet “hang time” to increase the probability our projectile will hit the target at unknown distances. Click. Boom. Hit. So why not 4.5 inches up and down if the average head is 9 inches tall for an MPBR of 349 yards!? Why not a 3.5 inch zero for a 7-inch diameter vital zone!? Sure, you can do that. It’s all up to you and it all depends on your expectations of precision vs the diameter of the target.
Remember that standard zero’s are made for shooter convenience and not what’s best for your rifle and projectile combo. Ranges come in known distance increments and we pick a set distance to zero out of convenience. That 50 or 100 yard zero for your setup doesn’t stretch out the rifle or carbines maximum useful trajectory. So what should be our goal when we zero?
Goal: increase the probability that the projectile will intersect the target *without* calculations.
Factors: Rifle and bullet accuracy, shooter accuracy, target size, and environment.
A defensive target, once engaged, will not stand up waiting to be shot. They will be hiding, returning fire, and they will present a small target for the shooter. Three inches of rise and fall (for a total of 6 inches of vital zone) gives us a great starting point for hitting hiding, peeking, or partially exposed targets. So instead of estimating range in a quick, violent engagement, I want to hold dead on and know that if my target is inside of 300 yards, that target is gonna get hit. This simplify’s ranging immensely. No holdovers. No hold unders either. My only question “is the target inside of 300 yards?” Yes? Then just a dead hold.
Six inches of total vertical resolution seems like a logical choice for an MPBR setup and extends us past our 50 yard / 200 yard zero a bit and is still a fine resolution for engaging defensive targets. I can’t think of anything I would shoot at that would be missed because my trajectory apex is three inches high. Look at your knee. It likely has a targetable area of at least six inches. Torso? This 6 inch resolution is easily inside the vital zone of a center of mass hold.
So next I whipped up a basic chart to get an idea of what zero at 100 yards I would need to get an MPBR which targets a 6 inch radius.
XM193 and Mk 262: Sight in at 100 yards X inches high in blue for a bullet apex of 3 inches; the MPBR is in red for each barrel and projectile. The XM855 would benefit at similar zeros as it will be in between the MPBR of the 77 grain and 55 grain ammo.
So you can see there is a bit of difference in the MPBR between rifle, carbine, and bullet. At one end we have the longer point-blank range of the 55 grain XM193 and at the other end the heavier 77 Mk 262 at the other. With modern ballistic calculators such as Strelok, you can simply zero at 100 yards, input the maximum target diameter, take the recommended zero for your new MPBR and Strelok will tell you how many clicks up from 100 yards to achieve that zero goal.
This method of sighting in gives you some excellent hit probability. If the target is near, a dead hold will hit anything in your maximum point blank range. If you estimate the target is at 300-400 yards, holding on the head will ensure rounds drop into the mid torso. If you were incorrect and your target was closer than you estimated, your projectile would still likely hit the head.
It appears that M193 or, even better, a quality defensive 5.56 equivalent such as Hornady 55gr TAP would make the best choice because of the high velocity achieved by 55-grain loadings… but when wind is thrown into the equation the 55-grain stuff makes it more difficult to hit the small targets at the end of its MPBR. So let’s look at heavier match bullets, what benefit do they offer? Increased accuracy and increased wind resistance.
Adding the Variables; wind, accuracy, and MPBR
Typically M193 is considered a 1.5 to 2 MOA load and the 77 grain Mk 262 is considered a sub MOA load. Think of each bullet as a probability to hit an area based on its accuracy. Groupings are the defining measure of whether an MPBR zero will be effective as inaccurate ammo could possibly land too far away from our target radius to remain useful. If your gun cannot keep groups inside the defined zone, then the distance you have chosen won’t work very well since trying to keep the bullets in a 6 inch diameter target zone out to 300 yards won’t work if your rifle is shooting minute of barn.
Ideally, you should start with an accurate, free-floated barrel, and use the best ammunition available to you. A rifle shooting terrible groups at (Say 4 inches at 100 yards) will not benefit from MPBR, as we must consider that at 200 yards the groupings would double to 8 inches, and at 300 the groupings would run around 12 inches. This eliminates the gains of our MPBR since many of these shots will escape our defined target zone due to simple inaccuracy. A match projectile on the other hand, which shoots 1 inch or less at 100 yards, 2 inches at 200, and 3 inches at 300 will remain useful inside our maximum point-blank range.
Wind can cause us a horizontal shift away from our intended goal of hitting the target. With our example of a 6 inch diameter target and a MPBR of 300 yards, I still want to be able to hit the target in a slight wind. The benefits of match ammo are two-fold: better wind resistance and tighter groupings. Both of these characteristics are just what we want when setting up our rifle or carbine. In the 20 inch gun, the Mk262 gives us an MPBR for our six-inch diameter target of 284 yards which sacrifices 16 yards from XM193… but the gains in accuracy and wind deflection make it the logical choice for a shooter who wants statistically significant gains on hit probability. As long as you do your part and shoot well, the higher accuracy and better wind resistance will reduce flyers which could land outside our intended target.
So ultimately, your shooting goals should play into the rifle and its associated setup and upgrades. A red dot or BUIS set up with a MPBR zero will assist you in hitting targets of opportunity and at any distance inside your MPBR “box”. Since we cannot effectively range estimate every shot on fleeting targets, best practice would be to utilize MPBR to ensure hits by maximizing projectile trajectory as it relates to the size of our target. This method may be off-putting to those with an ACOG or similar rifle optic since it negates the benefit of the bullet drop stadia. We don’t need any BDC stadia to be riflemen. We need knowledge and best practice methodology to ensure hits at any distance.
Best practice appears to be a heavy match bullet out of a rifle length platform to maximize the flat trajectory of the projectile and to take advantage of better accuracy and wind deflection. This should increase your success in hitting targets with less correction.
The true value of this setup is that it helps free you from thinking about your target distance in hundreds of yard increments, and instead it allows you to estimate either near or far. Is the target inside of my MPBR? Yes? Point. Squeeze. Hit.
Integrating this into my setup… I foresee finalizing my optic equipped rifle with two loadings: XM193 for practice, and Hornady 75 gr HPBT for longer range work. The Hornady is considerably cheaper than the 69 grain SMK I have been shooting, and switching back and forth between the two loadings is as simple as uncapping the dial and rotating in a few clicks of elevation and windage. I think these loading’s can cover all shooting I can ever realistically do. I really like this method as it increases the probability of intersecting the target at x range inside my MPBR zone. It’s important to get away from the 100-200-300 yard paradigm and examine a zero which allows a more fluid approach to hitting a target at unknown ranges… because remember this, if nothing else; every field target will present at an unknown range.
The goal of a marksman is to study the platform and integrate the best practice findings into his or her shooting. I think it is safe to say that for work inside of an MPBR of 300 yards, the 77 grain Mk 262 offers the best probability of hitting the target if shot out of a rifle length system, and its excellent characteristics make it best for environmental conditions. XM193 makes a good substitute as your holds would be the same, but the wind may knock you off target without some very light wind correction.
If you are interested in a more standard AR15 zero method, check out the article linked and visit Soldier Systems.