I have been testing rifles and optics for a living for several decades now, which means I have zeroed a lot of scopes. As a result, I have developed a method to do this very quickly—a process you can learn and use yourself. Here's how to zero your rifle scope quickly without wasting time or ammunition:
The Right Distance
I prefer to initially zero any rifle at 100 yards. Most ranges are set up for this distance and most scopes are calibrated to work well with that range.
Using a closer target may hide mistakes or problems. A more distant target can magnify shooting errors or allow environmental influences, like the wind, to skew the results.
If you prefer a longer distance zero, allow for that by placing your point of impact higher on the target at 100 yards, and then confirm later at your chosen distance.
For example, for a .308 with a 168 grain target load and a 200 yard zero, the point of impact will be 1.9 inches above the point of aim at 100 yards. The information on how high it should be above point of aim is available with any of the multitude of apps, programs or charts on rifle ballistics, so Google is your friend here.
Use a Bore Sight to Get On Paper
Make sure that the scope is bore sighted to the rifle, so it will at least hit the paper. There's nothing more frustrating than putting your reticle on the bullseye and not even seeing a hole...anywhere.
I tack up four targets with their edges touching so there is no space between them, and then shoot at the junction of the four. If the optic is correctly bore sighted it should hit someplace on the targets, and you can begin your adjustments from there.
Another way to do this with a bolt action rifle, an AR, and some shotguns, is to remove the bolt, put the rifle on a rest, and physically look down the barrel and get it in line with the target. Adjust the scope until you see the same thing as you do through the bore. This should at least get you on paper
When In Doubt, Get Closer
If you're still having trouble getting started, shoot at 25 yards to get a shot on paper. Just remember, your adjustments will need to be multiplied by four at this distance. If four clicks are one inch at 100 yards it will take 16 clicks to move an inch at 25 yards.
Use A Proper Rest
The only way to zero any firearm is to shoot from a proper rest that will completely support the weight of the rifle. This is not a test of your shooting ability; it is an adjustment process for a precision instrument. You eliminate human error as much as possible.
Use a shooting bench and sand bags, a Lead Sled, or another appropriate rest to zero an optic—not the hood of a truck.
While they might work in a pinch in the field, rolled up blankets and backpacks are a poor choice. Either use a commercial rest or make some sandbags, or buy a set, like these from Champion.
Use it Right
Support the forend of the rifle as well as the buttstock. Always support the forend, never the barrel of the rifle. The rest should be solid but with a bit of give, like a sandbag. This applies to both the front rest and the rear support under the toe of the stock.
Your job is to aim the rifle and then pull the trigger without disturbing that aim. You should not support the weight of the rifle in any way, that's what the rest is for. When you try to hold the gun, you introduce movement, and we don't want that.
Set your scope on its highest power. Aim for the center of the target and carefully fire a shot.
If it’s on the paper, fire two more for a total of three shots.
If you only fire one shot and you are flinching, or if the gun has some problems that are affecting accuracy, you can spend all day chasing bullet holes and never get the gun zeroed. Three shots will show any problems with your shooting technique or with the rifle right off the bat.
If the group is as expected, something under two inches, you know the equipment is functioning properly and that you are shooting correctly. If it is a lot larger, then you have a problem with shooting technique or your equipment. Stop and correct that problem before attempting to zero the rifle.
Remember, at this point we're concerned with groupings, not where the shots hit in relation to your point of aim. Your job is to keep the point of aim consistent for all three shots. It doesn't matter if all three shots wind up high left, as long as they all end up high left and close to one another.
Analyze Your Target
Find the center of the group and measure straight across, left or right to the vertical center line of your aiming point. If you are shooting at a single target it will be a line straight up and down from the aiming point. Eyeballing it and trying to draw a line with a pencil probably won't cut it, so bring along a straight edge, a marker, and a tape measure, which you should always keep stowed in your vehicle or range bag.
Once you have measured from the center of the group to the vertical line, record your measurement. Now measure up or down to the horizontal line indicating the center of the point of aim and record that number, like plotting a point on a graph.
Find the increments of adjustment for your scope. It should be marked on the adjustment turrets or on the dust cap that protects the turrets.
Most will be ¼ inch or ¼ MOA, which for all intents and purposes is the same. In inches, one click will move the point of impact .25-inch at 100 yards. One MOA is 1.047 inches at 100 yards. With MOA adjustments, one click will move the point of impact .26-inch. We can ignore the extra tenth of an inch here.
Some scopes have metric designations while others are in milliradian. In that case you must figure out what the adjustments are and do the math to move the correct amount on the target.
One milliradian is 3.6 inches at 100 yards. Most scopes are calibrated to 1/10th of a mill per click, so one click will move the point of impact .36-inch and three clicks will move the point of impact 1.08 inches at 100 yards.
If the scope is calibrated in metric, one centimeter equals 0.39-inch at 100 yards, so three clicks will move the point of impact 1.17-inches at 100 yards. Or you could measure your target in centimeters, if they're marked on your tape measure.
Once you understand the adjustment system, do the math for the number of clicks needed in each direction to cover the distance from the group to the vertical or horizontal line on the target.
Now make those adjustments very carefully. Stay focused, as it’s easier than you think to get distracted and mess up the count as you turn the dials.
Give it a Little Tap
My friends at the optics companies disagree with this next step, saying it is unnecessary; but it hurts nothing and I have found it to be a benefit with many low priced scopes and even with the occasional high priced scope. Use something soft enough to not damage the scope, like a plastic pocket knife handle or the lead tip of a cartridge and gently tap the adjustment rings of the scope. Sometimes the internal parts will stick a little after adjusting and this helps them settle.
Once you've made the adjustments that should bring your scope on target, fire another group of three shots. Another reason to shoot three-shot groups: if your first shot hits about where your first group did, but the next two make a dramatic shift toward the point of aim, the scope is sticking. The recoil from the first shot jarred the scope enough to allow the internal parts to move. This is far less of a problem than in years past, but it still happens.
This is another reason we always use three-shot groups, and measure from the center.
The center of your second group should hit at your desired point of impact. If not, then you just learned one nasty little secret about rifle scopes. They don’t always move the point of impact the distance promised.
Again, this is lot less common today than even a decade ago, as scopes are constantly getting better. It’s also something you run into more with inexpensive optics.
In this situation, you must measure, adjust and shoot again. Rinse and repeat until you are centered on your desired point of impact. Also, take it as a lesson that with optics you get what you pay for and while expensive, the better scopes cause less heartache. “Buy once, cry once” as they say.
I always like to shoot a few more groups just to prove the zero and to get a little practice with the gun before hunting.
Let the barrel cool before firing your final group to see if there is a point of impact change from a hot barrel. Remember you will always fire your first shot of the day from a cold barrel. Make certain that you adjust your final point of impact from the same cold barrel.