The purpose of sighting-in (also called ‘zero’) from a bench rest is to provide a stable and consistent platform for shooting a precise string of shots. It is from the bench that the shooter will be able to tell exactly what the rifle is capable of doing. The goal should be to shoot the smallest shot groups from a given distance, 100-300 yards (sighting-in), 400 to 1000 yards (field shooting); minute of angle or better.
Once you get a ‘minute of angle’ sighting-in (or better), you will then know what is the best bullet and powder combination or which brand of factory ammo gives you the best results.
Start where you get “on paper” (the target) with your rifle and scope firmly mounted and stock screws tight. Bore sight the rifle, using a bore-sighting device, (recommended) before you fire that first shot from your rifle. This is the first step to getting the bullets to hit on paper.
You can also bore sight your rifle the old fashioned way by viewing the target through your rifle barrel, provided that it is a bolt action rifle. First, make sure that the rifle is unloaded. You will need to remove the bolt and view the target and it’s red bulls-eye by looking through the bore of the barrel. You can then make adjustments on your scope so the cross-hairs are centered on the red bulls-eye. Having the rifle bore sight is the best place to start, as it will save you time and ammo.
Once your scoped rifle has been bore sighted, go to the 100 yard shooting position. Put up a large paper target. Use the Outers “Score Keeper” target or similar target with the one inch grid lines making it easier to see how far your bullet holes are from the point of aim (center of the red bulls-eye) using your rifle scope and spotting scope. Get yourself really comfortable on the shooting bench, so that you are totally relaxed and have no tension. Bring a foam sitting pad to sit on. You must use a commercial rifle rest, shoot off of a bipod on the rifle and a sand-sock (recommended), or sandbags to support and rest your rifle. Never rest the barrel on a hard surface. Rest the front end of the stock on the soft part of the commercial rest, or on the sandbags. When the rifle recoils, the rifle will have a consistent slide to the rear giving you perfect points of impact on the target. Clean your rifle frequently, following the barrel cleaning methods from the barrel cleaning page.
You should be using a variable power scope, set to the highest power possible, and still be able to see the target clearly. Adjust the scope including the objective lens adjustment, (turning knob at the front of the scope). Get to know your rifle and scope and what your eyes like. Once you are in a steady sighting-in position on the shooting bench with the rifle pointed at the 100 yard target, load one round at a time and prepare to shoot. Put the cross-hairs directly on the center of the red bull’s-eye. Carefully fire three shots, using your best bench technique, and CALL the shots. That means if you “flinched” during a shot, call it a flinch, and carefully shoot the shot over again. And if the shot felt good, then call it good, and move on. Allow your rifle barrel to cool between shots. If the cross-hairs of the scope was on the center of the red bull’s-eye when the gun fired, you will know it. Go for the surprise trigger break. Examine the target and find the bullet holes. You should be able to see them through your rifle scope, or through your spotting scope.
Even though you bore sighted your rifle, the bullet holes are probably not going to be in the center of the target at 100 yards, but they should be on the paper. Measure the distance from the bullet holes to the center of the bull. For example, three rounds shot, hit 2 inches low and 2 inches to the left of the center of the bulls-eye. Adjust your scope the number of clicks required to move the point of impact of the bullets “up” and to the “right” to get to the center of the target. For example, your scope is 1/4 inch MOA at 100 yards. This means that each click moves the point of impact in 1/4 inch increments at 100 yards, so in order to move the bullet impact to the center of the target, we need to go 8 clicks to the right (windage knob), this puts the impact centered under the red bull’s-eye.
And to further save ammo and time we want to be 3 inches above that red bull’s-eye at 100 yards to bring out the maximum distance of the rifle cartridge, (maximum point blank range or MPBR) eliminating the need to “hold over” on any big game animal. In a hunting situation, even though you have a range-finder, you may not have the time to use it to know the exact distance. Your concern is to hit the vitals of the game you are hunting. This is why you want to use the farthest, optimal distance in sighting-in your rifle. We were 2 inches low plus the 3 inches we need to be high. So we go up 5 inches or 20 clicks (elevation knob), and carefully fire another three shot group. Once that three shot group is carefully fired, we should have three rounds, grouped close together, three inches above the red bulls-eye, and inside of a one inch square, or better yet, all rounds inside the top half or the bottom half of that same one inch square.
During the sighting-in process, if you were carefully shooting your rifle, and the best group you can get is 1.5 inches to two inches at 100 yards, then shoot your rifle again and if it’s the same thing, then look at having a bench rest shooter shoot your rifle, and have someone look at your bench shooting technique, to see if you are flinching under recoil. Or look into getting gunsmith work done . DO NOT be satisfied with mediocre shot groups, besides, you won’t be able to progress into accurate long-range shooting.
Once your rifle is shooting three inches high at 100 yards consistently, you will have to decide at what distance you want your rifle sighted in at. You can move a new target out to the 200 or 300 yard range to get your “True” sighting-in distance, the final zero you use to hunt and shoot your rifle. Remember, when sighting-in, you must “verify” every distance you shoot at, and know for sure what your bullet is doing as it flies through the air, at any given distance. Use the same careful procedure of firing three carefully placed shots, allowing the barrel to cool between shots. The goal is to shoot a two inch group or better at 200 yards, and a three inch group or better at 300 yards. When you do. Shoot a final three shot group to make sure everything is consistent and you are Sighted-In!! You should be able to do this with a box of (20) cartridges or less.
The next step in sighting-in for hunting, you will need to get off of the bench and shoot from the field shooting positions, kneeling, sitting, prone, and standing, to see if your rifle will still hold it’s zero off of the bench. Be sure to hold and grip your rifle the exact same way, throughout all of the shooting positions to ensure same pressure and same point of impact, confirming your accuracy in each of the positions. Set up a picture target (card-board cut-out) of a deer or whatever animal you’re hunting at 200 or 300 yards (your zero) and carefully shoot a three shot group. Your shots should be evenly grouped on your point of aim. If the groups are much larger than MOA, think about trigger control and proper position and try again.
If you have cleaned your rifle five rounds ago or less do not clean your rifle anymore if you are going hunting, allow your rifle barrel to be “seasoned” with some “fouling” shots from when you were last shooting well. Carefully place your rifle in it’s travel case, and be careful not to drop it during your transport to your hunting destination. And ALWAYS shoot your rifle at your hunt destination, to CONFIRM your sighting-in process at the place where you will do your hunting.
Lets use the one of the .30 caliber magnums as an example; shooting a 180 grain Nosler Partition Bullet at 3,340 fps. Sighting-in 3″ high at 100 yards, you confirm the zero at 300 yards, then shoot at 400 yards and confirm that the bullet drop will be 8″ inches low at 400 yards. So, if a quick shot presented itself, and you don’t have the time to use your range-finder, no figuring would be needed, you hold on the center of the shoulder on a deer, anywhere from the muzzle to 350 yards, and you will hit the vitals area. If the buck is out at 400 yards, you can hold on the top of the back and hit near dead center. You bring out the cartridge’s full “point-blank” potential by taking the time to CONFIRM these distances. A weapon of this type has the potential to group 4 inches at 600 yards with dedicated practice.
Sighting-in your rifle is a important and necessary step in obtaining true accuracy in your long range shooting endeavors.
Other info:
http://www.achengineering.com/modular-clean-room-walls/
https://atlanticscale.com/history-of-gauge-blocks/