HOW TO ZERO A RIFLE

Choosing the best zero for your rifle

Here at Calibre we see a lot of information on how to zero your rifle. That's important information, of course, but a lot of the time we notice that the articles on zeroing a rifle start by assuming the ideal zero distance as an arbitrary given, whether they use 100 yards, 200 yards, or some other distance usually meant to approximate one of the above.

But choosing the right distance to zero at is as important as getting the zero right at distance. Simply using a 100 yard zero because that is what you've always done or because that's the longest distance your range can allow for is, in a word, silly. In fact, in many cases, zeroing your rifle to the popular 100 yard (or metre) standard may actually be hurting your chances of scoring that vital hit this hunting season.

Why? Well, because when you zero a rifle you're actually working with two zeroes, and a trajectory that deviates from those zeroing points before, in between, and after those two zeroes. To explain, consider a centrefire rifle with a scope mounted 2" above the bore, zeroed at 100 metres. At the muzzle, the round is 2" below the point-of-aim, due to the scope's height above bore. From that point, the round essentially rises vertically to meet the point-of-aim at 100 metres, and (in most cases) will continue to rise past 100 metres before it bleeds enough energy that gravity takes over and begins to pull it back down. For the purposes of simplicity, let's say the round continues to travel upwards until 200 metres, at which point it begins to fall downward. At some point in the downward portion of its trajectory it will again intersect the scope's point-of-aim, creating the so-called "second zero." The best zero for your individual rifle will be the one that minimizes the upward and downward deviation of the bullet's trajectory from your point-of-aim up to the maximum distance you expect to shoot.

So this being the fall issue, we'll start by looking at some popular rifles and cartridges and their best zeroes, and explain how to find the best zero for you.

The Lightweight

While not all provinces allow hunting of big game with the .223/5.56mm NATO, it's become so utterly ubiquitous thanks to the proliferation of AR-15s and their competitors that it's impossible to ignore.

The .223 is a flat-shooting round on account of its generally low-mass, high-velocity projectiles. Originally developed by the US Army as an outgrowth of the .222 Remington, the increase in case capacity that the military insisted on gave the cartridge the speed it needed to earn a place in history and, eventually, in the stables of many hunters of light game.

Owing to the extreme popularity of AR-15 accessories and similar rifles in shooting sports environments, we'll work with a 2.6" mechanical offset. If you're not shooting an AR, you'll have to adjust this; an AR-180b is fairly similar, for example, but a Tavor or similar is going to be significantly higher.

There are several approaches to zeroing the .223 for range or competition use, depending on your application. For this example, we'll use 55 grain standard Remington UMC or Federal M193 loading, because it'll line up very closely with most practice ammo. Out of a 16" barrel, both those rounds should be travelling right around 3,000 feet per second, or slightly slower.

One school of thought, which is largely derived from close-range shooting, is to zero at 50 yards, or 50 metres, depending on who you talk to. There's certainly something to be said for this approach simply because a lot of AR shooters won't shoot their .223s very far, and having a very concrete point of aim/point of impact congruity at close range is more important than knowing the exact location of the bullet at 200 yards. Furthermore, in most cases, the 200 yard zero is very close to the 50 yard zero, and there are a lot of people who consider them interchangeable, although they are not. For example, a standard 55-grain FMJ projectile leaving the muzzle at 3,000 feet per second on a rifle zeroed at 50 yards will hit 0.30" low at 200 yards, and 9.75" low at 300. Trade that 50 yard zero for a 200 yard zero though and you will still score great hits at 50 yards (specifically, 0.07" high, which we believe to be a statistically insignificant figure given we're not the Terminator or Chuck Norris), be spot-on at 200 yards, and almost half an inch closer to your point-of-aim at 300 yards. That's not necessarily critical and it's probably a smaller difference than the vast, vast majority of shooters could guarantee out of their own performance, but it's a difference of which you need to be aware.

If you choose either one of these out of varmint-style bolt action rifles, and are shooting heavier weight bullets with higher ballistic coefficients like Hornady's 60-grain American Whitetail round, you're looking at a trajectory that will probably start around two or two and a half inches low, peak at 150 or so yards, and fall pretty close to the point-of-aim until around 250 yards. Out of a 24" barrelled bolt-gun, that American Whitetail with a 50 yard zero generates a deviation of 1.5" high between 100 and 150 yards, 0.72" high at 200 yards, 6" low at 300 yards, and 20.8" low at 400 yards. Conversely, zeroing at 200 yards generates a deviation a 0.19" low at 50 yards, roughly 1" high from 100 to 150 yards, 2.71" low at 300 yards, and 22.26" low at 400 yards. Obviously which zero you prefer will depend on where you do most of your shooting; inside of our outside of 200 yards.

The Cowboy Gun

The old cowboy favourite, the .30-30, or .30 Winchester Center Fire, is still a popular round for hunting in dense brush where long range shots aren't a key consideration. Typically packaged in light, handy lever action rifles, this makes a great deer round, and don't let anyone's marketing department tell you different. Originally a black powder round (a .30 calibre slug over 30 grains of black powder), it's soft-recoiling even in a fairly light gun, and combined with the inherent speed of a lever action it allows quick and comfortable follow-up shots.

Of course, the downside to the soft recoil is the relatively slow speed of the projectile, and this is often combined with ballistic coefficients that are closer to pistol bullets than modern rifle bullets. So the zero will have to factor in the relatively steep drop of the bullet past 150 yards.

Our most likely use for a 30-30 would be at or under that distance anyway, but just to be on the safe side, we'd prefer to have the ready ability to underestimate the distance by a couple of dozen yards without paying too high a price, so let's make the goal to maximize the simplicity of use within 250 yards, but with a focus on 150 and below. Thankfully, with the 30-30, that's pretty simple.

If we're using an iron-sighted rifle, the sights are extremely close to the bore; we'll say half an inch. But even so, the popular 150 grain round nose .30-30 round gives us a whopping 16 inches of total drop over 250 yards, so we need a zero distance with those half-inch over bore sights that'll give us a good flat arc for as long as we can get it. Adding a scope typically would change things slightly insofar as it increases the height over bore of our sighting system, which in most rounds would have dramatic effects on the distance at which it should be zeroed, but due to the relatively short range of the .30-30 has surprisingly little effect on the ideal zeroing distance.

Which brings us to the next factor in choosing the best zero for your rifle: The size of your target. After all, if we are choosing to compromise on our zero by selecting one where the up/down deviation is mitigated within the ranges we expect to shoot, we're also conceding that we might be taking shots without dialing in proper elevation corrections (as doing so would negate this whole purpose of this article). So if we're not dialing in our ranges, then the size of the thing we're trying to hit begins to play a role on our best compromise zero, as the size of the target essentially provides boundaries for how high above the point of aim, and how far below the point of aim remains acceptable to score a meaningful hit.

Now, in the case of the .223 this wasn't much of an issue by virtue of the round's flat trajectory and varied use as both a sporting round, a varmint round, and in some cases a big-game round. But the .30-30 is far less flat-shooting and far more specific in use; it's a deer gun. So, given a deer's vital hit region is about 8" across, zeroing your scoped .30-30 to a relatively surprising 180 yards, will yield the best results. Why? Because zeroing at that range will give you a gun that shoots 2.15" high at 50 yards, 3.85" high at 100, 2.54" high at 150, and 2.51" low at 200. In other words, so long as you hold dead on the vital area of a deer, you'll score a good hit anywhere from point blank out to 200 yards. If you're using iron sights, technically bringing the zero in a wee bit to 170 yards will keep you inside the vital zone right up until 200 yards, but will have you brushing up against it at 100 yards (where you'll be 3.89" high) and 200 yards (where you'll be 3.94" low) so we recommend favouring a 150 yard zero at that puts the round just 2.5" high between 50 and 100 yards.

Granted, it drops the round over 6" low at 200 yards, but that's also a pretty long shot with buck fever and iron sights. If you're wanting to lure them closer for your shot, you may want to consider taking a look at what they've got over on Feed That Game to see about setting up something up close and personal.

Okay, the .223 made you wince with pity, the 30-30 is for old, busted up cowboys and the .308 is for people with a recoil allergy. You only hunt with a gun because you can't get close enough to a moose to just punch it to death, so the kick of a rifle means nothing to you, and as a result you shoot a .338 Winchester Magnum.

Interestingly, this is the point at which it should all start to come together: the monster .338 actually performs quite similarly with typical loads to other relatively modern calibres. If we take a look at Hornady's mighty 225 grain SST, (which develops a staggering four thousand foot pounds of energy at the muzzle and retains more energy after a kilometre than a contact shot with a .44 magnum) the trajectory is not really that exotic. If we use a typical offset for a scoped hunting rifle, a 200 yard zero is about perfect: at a hundred yards it's less than two inches high, and less than three inches low at 250. It's really not until 350 yards that it starts to get into dialing elevation on the optic, hitting about thirteen inches low. It's a fairly familiar path. But, at the same time, when you start getting up in calibre you're typically looking at longer shots on larger game with bullets of far more various weights, making your specific zero something you should consider tailoring to your rifle, load, and optic. But how do you do that?

Getting a zero is science; picking a zero is art. You need to balance the terminal performance of the round at different ranges with the trajectory of the bullet and the target zone you're shooting at; our preference is ordinarily to extend the point-blank range as long as possible and keep the bullet within a fairly narrow cone of fire. There are specialist zeroes for long range, for particular target shooting disciplines and for various combat applications, but in general, for most people, most of the time, extending point blank is a good approach. And mathematically, it's not a complex equation, as it simply requires the tabulation of the bullet's trajectory, and some arithmetic involving the standard deviation of the round across distance, the height over bore of your optic, and of course the target size. Simple right?

Thankfully, through the miracle of the internet, you don't need to know how to do it... you just need to know how it works. Our favourite system is the simple Ballistic Trajectory and Point Blank Range calculators located on the excellent (and free) website, shooterscalculator.com. Inputting the ballistic coefficient of your bullet, its muzzle velocity, the height over bore of your optic, and the size of your target into the Point Blank Range calculator will give you the mathematical "perfect" zeroes that'll keep your round inside the vital zone for as long as possible, while the Ballistic Trajectory calculator can allow you to visualize that data and see how any modifications to the round or your zero may affect performance. You can even input your altitude, average humidity, and average atmospheric density to fine tune the PBR and trajectory calculator outputs to your specific situation. But while all this technology may be great, the most important thing is that once you've picked your zero, you get out and shoot your rifle at all ranges. Because the one thing you don't want is a ballistic surprise during a critical shot.