Ground zero: put your rifle on the money with no muss, no fuss.
Before you head to the range, there are a number of things you need to do. First, you need to make sure you have a solid, firm support for the rifle's fore-end and buttstock. A commercial adjustable fore-end pedestal topped with a small leather bag filled with fine sand, and a "rabbit ear" or "bunny ear" rear bag for the buttstock are best--although you can make do with the small sandbags and wooden pedestals that you find at some public ranges.
Another option is a self-contained unit like the MTM plastic Predator Shooting Rest shown in the accompanying photograph. Lightweight and relatively inexpensive, the Predator's pedestal setup puts the shooter in a good, upright position to absorb recoil. The forward pedestal is screw adjustable for height. Similar products are available from a variety of shooting products companies.
If you want to save a lot of time and a lot of shots, make certain everything is secure before you head to the range. After ensuring your rifle is unloaded, check all the mount screws, and you may even want to remove the scope to be sure the base screws are tight.
I also recommend removing the barreled action from the stock on guns that allow this. Look over the bedding and remove any loose wood or fiberglass chips. At the very least, take a screwdriver to the action screws and check for proper tension.
It may sound basic, but another thing you should do is determine the adjustment increments in your scope. Most scope clicks or increments are a quarter-inch at 100 yards. Some are a half-inch and some are a third-inch, depending on the scope make and model. Do this at home in case you need to refer to scope literature to find out. Sometimes the increment is marked under one of the scope knob covers or on the knob itself.
One last chore. If you are dealing with a semi-auto or lever gun where you cannot easily remove the breech bolt to look through the bore, you can use a collimator to get the bore and crosshair intersection aligned as closely as you are able.
If you do not have a collimator but have a bolt action rifle, you can bore sight at the range. Observing safety rules (like never sitting at the bench with a rifle when someone is down-range), place your rifle on fore and aft shooting rests with the gun pointed downrange and the bolt removed.
With the rifle solidly rested and the target aligned in the center of the bore (black bullseye targets are best for this), rotate the scope adjustment knob until the crosshair is pointing at the center of the target--with the target still centered in the rifle's bore. The rifle will likely shift position when you turn the scope knobs; simply go back and realign the bore and recheck the crosshair alignment.
Repeat this process carefully, making certain that you are looking right down the center of the bore and that the bore is exactly centered on the target. It does not work to move your head to align the target. You need to move the rifle until the bore is perfectly aligned. Once that's done, you'll be on paper--all without wasting a round of ammo.
Now it's time to begin shooting. Ideally, the shooting table should be about chest high as you sit on the shooting stool. If not, you may be able to raise or lower the seat height. I have used a telephone book on a too-low stool. If you have a sling on the rifle, remove it so that it will not be in the way. Place the rifle on the bags and adjust the height of the forward pedestal to bring your crosshair in line with the target.
The buttstock should be supported in the sandbag rest. The shoulder simply comes forward to meet the buttstock when it is time to fire the rifle. The forward pedestal and rear bag should be adjusted so that the rifle tracks fore and aft in line with the target.
The rear bag and table height should allow the rifle's buttstock to fit snugly into your shoulder. If the rests are adjusted properly, sliding the rifle forward in the bags causes the crosshair to move downward. Sliding rearward causes the crosshair to rise on target, but the vertical crosshair should split the target as the rifle moves. Position the rifle and pedestal so that the sling swivel studs do not grab the bag during recoil.
If you have a rabbit ear rear bag, the buttstock tracks between the ears of the bag. If you have a relatively light-kicking rifle, say under .270 Win., position the non-firing hand on the base of the rear bag. Squeezing this bag lowers the crosshair on target. Just prior to final aiming, align the crosshair slightly above the aiming point, then squeeze the rear bag to bring the crosshair into final alignment with the target.
If you're shooting a hard-kicking rifle, you can move the non-firing hand to the fore-end behind the front pedestal to control the rifle and prevent it from jumping off the pedestal. But remember, aiming is done with the bags. It is not done by holding the rifle on target with your muscles or with shoulder tension. The firing hand pulls the grip straight back until the buttstock meets your shoulder with no twisting or torquing force applied to the grip.
The crosshair should be completely steady on target. When you are sighting in, the idea is to see where the rifle is shooting in relation to where the crosshair is aligned. Dry fire the rifle a few times to see if the crosshair moves on target as you pull the trigger. It shouldn't. If it does, adjust your setup and dry fire until the crosshair does not move on target when you pull the triger.
Again, make sure everything is clear downrange and it is safe to shoot. Now load the rifle with the ammunition you intend to use on the hunt, hold solidly on the aiming point and carefully squeeze off a shot. You should be on paper at 100 yards. Fire at least two more shots in the same manner before you make any sight adjustment.
Three shots are usually enough, but sometimes, after having removed the barreled action from the stock and the scope from the rifle, it takes a shot or two to settle everything in. You may need to ignore the first shot. After no more than a couple of shots, the rifle should cluster its shots reasonably well--say within two inches at 100 yards.
Determine the center of the three (or four) shots, make sight adjustments and fire again. If you're shooting a scoped rifle, it is convenient to use a target with one-inch squares in a grid pattern. This way you can see through a high magnification riflescope or spotting scope the amount of adjustment you need to make in your crosshair. If the scope has quarter-minute clicks, four clicks will move point of impact approximately one inch--one square--at 100 yards.
With American scopes (and some European scopes as well) you can think of the adjustments as screws with conventional right-hand threads. If you turn the top knob clockwise as if you're tightening it, point of impact will move in the same direction: downward. If you rotate the right side knob clockwise, point of impact moves the same way you are tightening, to the left.
If I am sighting in a rifle for big game with a modern, flat-shooting cartridge, I like to sight in so that bullets impact about 2 3/4 inches above my aiming point at 100 yards. If I am sighting in a varmint centerfire, I sight in one or 1 1/2 inches high for small varmints or coyotes respectively.
Sighting in an iron-sighted rifle is a different ball game. Here I would use a bullseye target for a well-defined six o'clock hold. Adjustments are made by tapping the front or rear sight laterally with a hammer and brass punch.
I like to zero an iron-sighted rifle dead on at 100 yards. Most of these guns are lever-action carbines chambered for relatively short-range cartridges. In addition, aiming with open iron sights is less precise than with a scope. The carbines are designed for woods hunting and shooting at shorter distances, usually inside 125 yards or so. This is why I zero an iron-sighted gun dead on at 100 yards.