Absolute zero essential on a scoped hunting rifle
by R.K. Cambell
Contributing Editor
A decade ago the late Col. Jeff Cooper noted he had seen a few men who were fine field shots but who fared poorly on paper. I have met a few of this breed but the fact is the only indicator of field performance is range work. Those wishing to properly utilize a rifle with an optical sight must invest time and effort to carefully zero their personal firearm. Despite advances in quality control and accuracy in rifles the final arbiter of success remains the operator. Good equipment cannot be overrated but in the end how we use our equipment matters the most. In the past we may have turned to a custom rifle and a good gunsmith and this is still the preferred route, but a number of perfectly good firearms are available straight from the factory.
Some are delivered with a bore-sighted optical sight but only the operator may zero the rifle for optimum use. There are numerous considerations when zeroing the rifle. Hopefully a cartridge suitable for the intended mission has been chosen. Popular general purpose cartridges include the .223 Remington, .308 Winchester and .30-06 Springfield. The intended use of the cartridge, the velocity achieved by the cartridge, and the likely scenario dictate the range at which we will zero the rifle.
As an illustration, those using the .30-06 Springfield may opt for a 150-yard zero and hold under at 100 yards, while holding over at 200 yards. Holding under or over simply refers to an allowance for drop in the cartridge at longer or shorter range than the piece is zeroed for.
Faster cartridges may allow more versatility. If you are using the beanfield as a yardstick then a 250-yard zero may be advisable. But be realistic. If your hunting stand calls for a 100-yard shot, then let that be your zero. Achieving a perfect zero and optimum accuracy may be challenging even at a relativity pedestrian 100 yards. Ammunition choice is important, nearly critical. Many shooters choose a factory product.
Excellent factory ammunition is available. Black Hills Gold is a standout, while Hornady’s Light Magnum maximizes the 6.5 Swedish Mauser and other true rifleman cartridges. We all wish to use a cartridge that is gilt-edged accurate but a combination of penetration and killing power is also important.
Just the same, Black Hills, Hornady and Cor-Bon, among others, have shown us that terminal effect and accuracy are not exclusive. An accomplished handloader may or may not produce drastic improvement but he or she is in a better position to work up the ideal load, achieving the key harmonic balance of accuracy and power.
When you mount an optical sight you are laying the foundation for accuracy. The proper mounting of the scope is vital to repeatable accuracy. But before you mount the scope be certain the scope rings are properly affixed to the receiver, concentric. Do not skimp on scope rings. S and K, Conetrol and Leopold are among our better makers with predicted good service. Kimber offers bases for their rifles that, like the rifles, are first class.
Once we have the scope properly and carefully mounted, we proceed to proper sighting. Removing the bolt and lining the bore on target, carefully moving the optical sight zero, is called bore sighting. While fine with a bolt gun bore sighting is problematical with an automatic rifle. You must get the scope properly attached and proceed to aligning the scope zero with means other than the bore-sighting. Bore sighting even with bolt action rifles is merely to give a rough approximation and get the rifle on paper.
I use a mechanical alignment device called the Alley Bore Sighter, a modern high grade collimator. This collimator attaches to the barrel via various caliber spuds that are inserted into the barrel. The sight reticule is aligned with the collimator into a zero that is often very close to the true firing zero. In other words, minimal adjustment will be needed on the range. A perfect zero is not in the cards with a collimator but often the zero is close. This saves much time and ammunition at the firing line.
The preliminary accomplished, we travel to the range for live fire work. When zeroing the rifle a comfortable, repeatable rest is important. A sandbag is ideal. I have enjoyed good results with range bags that support only the forend, and avoid a too hard rest for the forend. But a solid mechanical rest may absorb much of the recoil of a powerful rifle and allow more time in shooting before recoil begins to affect our results. The rifle should be on a level plane. The forend should be rested just behind the front sling swivel for best results. The support must be repeatable for each shot. This applies not only to optical sights but iron sights. I recently sighted in an M1 Garand and M1A1 Springfield using the same techniques I use for sighting in optical sights, as far as resting the rifle goes. Each uses match-grade, click-adjustable aperture sights. A steady rest, but not a hard rest, is needed. The process is less of a chore with the proper comfortable, repeatable bench rest.
When sighting the rifle in I fire first at 25 to 50 yards, depending upon the rifle and the mission. While this is short range for a precision rifle, you do not wish to be off the paper at 100 yards. Once a rough approximation of zero is accomplished or the rifle is in the black at a given range, we wish to move to the chosen zero range and manage the proper absolute zero. At longer range, any imperfection in the rifle sight or ammunition will be apparent. I fire three-shot groups to engage the target and carefully record the results as I move the zero. It is important to allow the barrel time to cool between shots. While some fire five-shot groups, five shot groups are more useful for checking accuracy potential than in working to achieve a zero, I fire three shot groups. I move the turret dials carefully until I achieve the desired zero. Sometimes, in order to avoid confusion, I will move only the elevation or only the windage turret and fire a shot or two in preference to moving both to a zero point.
Remember, elevation and windage are separate matters and one does not affect the other. Each is independent and the elevation zero or windage zero remains constant when the opposite number is set. The painstaking method is more time consuming, but in the end the zero obtained is more trustworthy and precise. With a minimum of shots we may move to the proper zero, which may range from 50 to 250 yards. As an example, the Ruger 77/22 we use for squirrel hunting is sighted for 50 yards. Our 300 Magnum hunting rifle is sighted for 250 yards.
A reason I especially appreciate the mil dot reticule of the Mueller scope is that a skilled user may instantly choose the proper bar for a range other than the distance at which the rifle is sighted. Simply shifting focus allows a good hit. Similarly, high velocity cartridges allow an easier hit. Depending upon the caliber and rifle, exact zero and range estimation may not be critical. As an example, a whitetail deer offers approximately an 8-inch kill zone. We like to be precise but this is a lot of area into which we may stuff our Nosler Partition bullet. If expecting a shot from 100 to 200 yards, a 150 yard zero is a sound choice. Be certain you are familiar with the bullet’s point of impact versus point of aim at other distances.
A competent rifleman may elect to pre-select click-adjustment increments for different ranges. While an expert rifleman may enjoy firing and experimenting in 25-yard increments most of us will be limited by time and skill to 50-yard drills. The 50-yard drill increment is simply more realistic. If you envision firing at greatly disparate ranges, say, from100 to 400 yards, then a card taped to the stock with the proper “clicks” recorded is essential. The note card should clearly spell out that you must move the elevation four clicks to the positive. But do not neglect to make the table run in both directions. In other words, if you click to 300 yards, be certain you have the card properly filled out to run back to 100 or 200 yards. You may be as thorough as you care to be with this information and it will pay off if you do any amount of shooting. The results of range work should be inscribed on this card and also on a copy for safe keeping.
Same Load
It goes without saying that you must stick to one load when using this card or you will have to begin again. I would have to discover great accuracy or performance advantages to switch from my current up and ready .223 Remington, 5.56mm and .30-06 handloads.
There are alternatives to the range card. I have used the ATN scope for some time with my personal Bushmaster carbine. This 16-inch carbine is surprisingly accurate, although I admit to a few simple upgrades. The ATN features a ranging knob that allows the shooter to dial in the range from 100 to 300 yards. Simply click to the desired range and you are on the money. I admit I was skeptical at first but if the rifle is properly sighted, first for 100 yards, the scope works great with both 55-grain general purpose loads and Black Hills 60-grain JSPs. The 5.56mm is a flat shooting cartridge and the ATN scope is a great match with the Bushmaster.
Another alternative is the Drop-In-Sator (PO 2372, Eugene OR 97402; phone: 877-376-7467; online: pacinfo.com) for range. The Drop-In-Sator is available for most popular scope and rifle combinations. The turret cap is fitted by simply screwing it on after you have sighted the rifle for 100 yards. Then, use the proper calibrating sleeve for the load you are using and you turn the adjustment knob to 300 yards and you are dead on. Some sleeves are made for 500-yard range, but I find the 300-yard calibrating cap most useful.
There are other problems that should be addressed. When pursuing top accuracy I doubt many of us will use the popular forward vertical hand grip for the AR-15, but I think that this hand grip should be avoided. This hand grip has been found to flex the barrel of the AR rifle, and the barrel locks into the steel bolt. When the barrel is flexed, the bolt will not strike the barrel properly and the bolt may be broken. This type of damage has been reported too often. All combat weapons are high round count and we must not allow a perceived advantage in rapid fire to intrude on reliability. Likewise, if you fit a custom stock, be certain that the stock does not affect point of aim and point of impact.
I think that a caution should apply to all shooters. While some bipods are great instruments—I have used the Harris extensively—others are not well suited to precision shooting. Some are more sensitive than others and the results of resting a bipod on a hard surface should be well understood.
With these thoughts in mind let’s look at the actual process of sighting in.
Getting comfortable: When bench resting the rifle be certain you are good and comfortable and firing from a solid rest. The recoil of the rifle should be well distributed on your shoulder. A recoil pad or shooting rest is a good idea with calibers above the .223.
Experiment with cant: Reading is great for all of us but problematical calculations must be proven on the firing line. There are a number of devices that allow a skilled shooter to fire more accurately. As an example, canting the rifle or scope may have an adverse effect on the rifle’s accuracy. A lack of cant is essential when the rifle scope is first mounted. When firing at moderate range the effect of a canted scope is noticeable. Paper calculations and trigonometry don’t work if the scope is off center. Canting seems to make the rifle shoot low. A rule of thumb is that canting seems to give an inch off the point of aim per 100 yards with a modest five degree cant. A variance of one inch at 100 yards, two at 200 yards and so forth results in a miss at longer range.
Recently I used my personal Howa rifle in a simple test. The load was the Sierra 52-grain Match over WW 784 powder. I also used the factory-loaded Black Hills 52-grain match load (which uses the same Sierra bullet). I would like to say my handloads were more accurate but at the best they were comparable, with either load producing a three shot .5 inch 100-yard group; all we can ask for. With a five degree cant my groups at 200 yards not only impacted three inches to the right of the point of aim but three inches low. This is enough to miss a coyote with a chest hold, or at least produce only a wounding shot. A five degree cant is not necessarily noticeable until you begin shooting but a ten degree cant should be obvious to the eye.
Testing for Repeatability
It is interesting to note that the problem of scopes losing their zero is less today than at any time in the past. The latest scopes are quite simply wonderful optical instruments, with good features and the best mirrors and turrets that technology will allow. The Leopold Vari X is a modern marvel. But just the same, a simple test of repeatability will prove out the quality of any rifle scope. We begin by firing a careful group at 100 yards. The three shots in the center are our mark. To begin, we move the elevation turret up two notches, then fire. Next we move the elevation turret down four notches and fire. Next we move the elevation turret two notches up (to original zero).
Next move the windage turret two notches to the left and fire. Then move the windage turret four notches to the right and fire. Then move the turret two notches or clicks to the left and fire. You should have an extra hole in the original group and four evenly spaced bullet holes in practically perfect squared alignment over the original group. If not, your scope has a problem with repeatability of adjustments.
When shooting in the field, you may find the rifle fires to a different point of aim than in range shooting. This is to be expected. You should fire in field firing positions at the range. A rule of thumb: when firing uphill or downhill, drop is canceled. Practice firing offhand, from a common field rest, such as a tree stand or a back pack, and consider your likely field problem.
Modern gear is just fine but in the end it is the shooter behind the sights that makes all of the difference in the world.
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