Point of Aim/Point of Impact
Once you have sighted your rifle in at a known distance, you have achieved point of aim/point of impact.Point of aim is using the reticle crosshairs as your aiming point, point of impact is where the round will strike your target. If you have sighted your rifle in at 100 yards, your point of aim at 100 yards will be the point of impact of the bullet. Knowing how your rifle cartridge behaves in regards to ballistic trajectory now becomes a factor if you need to shoot closer than 100 yards or farther away.
By adjusting our aim point without manipulating your scopes windage/elevation knobs, you are using ‘Kentucky windage’ to adjust. If your rifle/scope combination is sighted in for a different distance, this information will change. There are applications for smart phones and computer programs available to assist you with that endeavor if you decide to use a different point of aim/point of impact.
Let’s say that you want to adjust your scope by using the windage/elevation knobs instead of using Kentucky windage to correct for bullet drop at the range of 400 yards. By manipulating your scopes elevation knob using the example of scope ‘A’ from above, each ‘click’ will raise the impact point up 1 inch (¼ inch at 100 yard, 1/2 inch at 200 yards, 3/4 inch at 300 yards and 1 inch at 400 yards). So to raise the point of aim to reflect the point of impact, you would have to apply 24 ‘clicks’ to your scopes up elevation. Be sure to know which way is the ‘up’ adjustment for your scope. If your scope has a mark with an ‘UP’ arrow, that’s the direction to turn the knob to raise the bullet impact up. Don’t laugh, I see a lot of people over think this operation. Just follow the marking on your scope to do what you want to have it do.
Most hunters use a cheat sheet with the ballistic information for the round they are using taped to the inside of the scopes dust cover. When the dust cover is open the ballistic information is printed on the cheat sheet for easy access. Range estimation is vital as well as knowing the size of your target.
Windage is more difficult to adjust for. At close range, a mild wind will not affect the impact of the bullet substantially. As range increases, the effects of wind increase due to the rounds loss of velocity. The only true way to learn your cartridges’ windage adjustment is to fire at distance on windy days, or doing research on the topic.
Leading the target is another use for Kentucky windage. If your deer is walking slowly across your field of view, you aim slightly ahead of the deer. The farther the distance, the farther ahead you have to aim. Usually, the deer will not be walking so fast that you need to adjust your aim point for movement. Do realize that the longer the distance from you, the longer the round will take to reach its target. Leading the target really should only fact in when you are shooting at a running animal.
I hope this series has helped to increase your knowledge of scopes and will help you to be better informed when making a scope purchase. If you have any questions regarding this article or about scopes in general or need help making your next scope purchase, please feel free to contact us at firstname.lastname@example.org.
A boresight tool can be helpful to you to align the bore to the crosshairs of the scope. The purpose of a boresight tool is to get you on the paper when you zero your rifle. It will not accurately align the bore to the scope it is simply an aid so you can more easily sight in your rifle when you shoot it.
The oldest method is the ‘eyeball’ method. Secure the rifle in a cradle, remove the bolt, look down the rifle barrel and center the rifle bore on a bullseye target at 50 yards. Then you adjust the crosshair reticle to the same point on the bullseye. Since you used the bore to sight in the rifle that is why it’s called ‘boresighting’. This method does not work with semi auto rifles, pumps, lever action and most pistols.
A laser boresight is inserted into the bore of the rifle and project a laser dot on a target. Then the shooter adjusts the scope to the dot. There are different laser boresights for different calibers. The laser is both mounted inside an arbor type item and inserted into the muzzle or as a dummy cartridge that goes into the chamber. The laser dot has to be projected onto a target at a known distance, usually 50 yards.
Boresighting will only get you on a paper target if done properly. It will not accurately zero any rifle. The only way to accurately zero a rifle is to shoot it with the specific ammunition you plan on using to hunt with. Boresighting will alert you to any mounting or scope adjustment issues immediately, saving you time, ammunition and frustration.
A small crosshair leveling level will be required to ensure that your crosshair reticle is level to the rifle. You can eyeball this process but each person is different and this will ensure level. Just like everything else we are doing to mount this scope, it will eliminate a variable. If your crosshairs are not level, as you adjust for windage and elevation, it will not be true to impact. If your crosshairs are not perfectly level, as you adjust for windage and elevation, it will go at a diagonal, not exactly straight up and down or left and right.
Once you have the proper mount location, boresighting done, the correct level and the optimum eye relief, your scope mounting is done. Congratulations! Now it is time to talk about fine-tuning the internal adjustments of your scope namely windage, elevation and parallax.
Mounting the Scope
Like purchasing a quality scope, don’t be cheap with your mounting system or it will cause you to have problems in the long run. Doing proper research, finding out what kind of mounts are available for your rifle and knowing how to properly mount a scope to your rifle can be a bit time consuming but ultimately rewarding. Remember that your choice of mounts is what connects your scope to your rifle. If you have a quality rifle and a quality scope but poor mounts that allow the scope to slide, loosen up over time and move with recoil or don’t hold true they will cause you endless frustration and can make you miss the shot of a lifetime.
This is the term used to describe the exact center of the mechanical range of adjustment for your scope. Even if you have purchased a brand new scope, it is recommended to confirm mechanical zero. All you have to do is to rotate your windage adjustment all the way to the stop, then count the clicks as you rotate the windage knob in the other direction. Count how many clicks or turns, divide that number in half and count that number back toward center. Then do that for the elevation adjustment. This will ensure that you have the scope reticle centered in the scope tube and allow you to make adjustments from a known point.
Some scope mounts require a set amount of torque for the screws. I strongly recommend that you purchase or acquire a torque screw driver. Once again, the scope mount is a vital piece of your scope. At any time, if you feel overwhelmed, just stop and take the rifle to a qualified gunsmith or professional for help. Better to pay a professional than to mess up a valuable scope or rifle.
Be sure to understand how your scopes mount works and always following the mounting instructions for your specific mount. I always test fit before I tighten anything. It is important to put the rings as far apart as possible. This will distribute the weight of the scope and allow for greater balance and stability. Be sure to check each scope ring for raised ridges or any manufacture defects that could cause pressure on the scope tube.
When you tighten the screws, be sure to use a cross over technique when you tighten them. Do not screw one screw in all the way and then do another one the same way. This is similar to tightening lug nuts on a vehicle tire. Tighten a turn per screw, work your way cross way to the other screws and be sure to do both the front and rear scope rings screws. Once all screws are snug down in the scope rings you can torque to specifications, if needed. You will be screwing and unscrewing these screws especially if you lap your scope so be sure to use the right screw bit size and be careful not to cross thread the screws.
Lapping the scope to the scope rings is a way to increase precision and to avoid scope misalignment issues. This operation might seem complex but it is not.
When you lap the scope rings, you basically are ensuring proper alignment of the tube, preventing any flex or distortion, tweaking or bending. Misaligned scope rings can dent the tube, cause adjustment issues by putting abnormal pressure to the scope tube or distort the reticle. It is very difficult to see any misalignment with the naked eye. A lapping tool will provide a visual indication of any misalignment.
There are point to point lapping alignment rods and bar versions. You use the alignment rods to ensure proper scope alignment. There are basically two pieces to a lapping kit, the alignment rod set and the lapping tool. The alignment rod set is either 2 pieces of metal with a point at one end or a bar. The lapping tool piece is a solid rod with a handle to hold and rotate the rod in the scope mount. Be sure to have the lower rings mounted to the rifle then put the proper sized alignment rods into the cradle of the lower scope ring and mount the upper rings. They make 1 inch and 30mm lapping kits, be sure to buy the right one for your scope and rings.
You mount the alignment rods in the scope mount just like a scope. If you are very lucky, there will be no misalignment of the points. Usually there is, so that is why you bought the lapping tool. Remove the alignment rods and mount the lapping tool in the scope rings. Remember, you do not want to be too aggressive as you smooth the inner part of the scope rings. You can’t add material, so remove it slowly.
The lapping compound used should be very mild. Once you have the lapping tool mounted and the scope rings properly tightened, use the lapping tool handle to rotate the lapping tool in the mount. This will remove any burs, smooth the inside of the scope rings and align the two mounts to provide a straight cradle for your scope tube. Unscrew the rings, check for alignment and repeat as needed. This process might sound excessive but you have a lot of variables in the scope mounting process and this will eliminate most of them if done properly.
At this point, you should have the scope mounted, the screws tightened but not finally secured, the mount lapped if needed. The scope mounts should be as far apart as possible; the scope should not interfere with the action and it is time to adjust for eye relief.
A good quality scope should be water resistant, fog proof and shock proof. A large selling point is coating on the optical lenses. The optical coating on the lens will maximize light transmission into the optics, reduce the loss of light due to reflection, add some scratch resistance and reduce glare. There are several levels of coating.
• Coated: There is at least one layer of protection on at least one lens surface. This can mean that only one lens has a coat.
• Fully coated: The scope will have a single layer on all air to glass lens.
• Multi-coated: The scope will have a single layer on all air to glass lens with multiple coats on at least one lens.
• Fully multi-coated: This scope will have multiple layers of coating on all air to glass lens.
These coatings are intended to help minimize scratches, fog and the accumulation of water on the lenses. No coating is 100% effective and depending on atmospheric conditions, environment and type of use these coating should at least help. It is smart to always purchase a scope within your price range that has the best coating possible.
You can also do other things to protect your scope and to ensure it is ready when the time to take that shot arises. The purchase of a scope cover to protect the mounted scope is a great idea. We all know the misadventures in hunting that can and will occur and its best to protect your investment. There are also lens covers that protect the lenses when not in use. Just a small investment of money can increase your scopes survivability and usability.
Eye relief is the ideal distance your eye has from the ocular lens to provide a full field of view through the scope. If you primarily shoot this weapon from a rest, your eye will be closer to the ocular lens than if you were shooting it off-hand. Your head and neck should be comfortable and you should have a consistent cheek weld (the position of your cheek on the gunstock) to ensure proper field of view. It is important to move the scope to your eye, not the eye to the scope. This will cause a neck strain as you bend your neck toward the scope to see through the lens. Adjust your scope to the most comfortable eye relief for the shooting position you believe that you will primarily use.
The longest eye relief for an optical rifle scope is about 4 inches. This leaves enough room for the rifle to recoil and not strike you, if you have the proper ring mounts and the scope is mounted correctly. The higher the recoil of the rifle, the longer the eye relief needs to be to avoid scope bite, that painful and embarrassing cut above your shooting eye. A good quality scope should allow you plenty of eye relief so as to be comfortable and safe while shooting.
The eyepiece is not the same as the exit pupil. The eyepiece holds the ocular lens just like the objective bell holds the objective lens. Most eyepieces have a fast focus adjustment to help correct the image seen through the scope and make it clearer for those of us with less than perfect eyesight.
The small circle of light that you see as you look through a scope at arms distance is called the exit pupil. The diameter in millimeters is the exit pupil size we discussed earlier with the formula objective lens diameter divided by the magnification equals the diameter of the exit pupil. So a 55mm objective lens with 5x power magnification will show you an 11mm exit pupil.
Now turn the variable scope power all the way up. Look through the eyepiece and you should notice that the exit pupil is a lot smaller. Try to imagine if you are now using that scope in a low light situation and have the power at maximum. That exit pupil will be dark and small, almost too small to use.
What is so important about the exit pupil? The larger the exit pupil in size the less critical the shooter’s head placement is. The distance from the shooters eye to the ocular lens with the exit pupil projected on it is called eye relief. The distance from your eye to the ocular lens in a low power setting allows for greater range of distance but the higher the magnification power the more critical your eye is to be exactly centered on the scope. At maximum magnification the exit pupil is smaller so your eye has to be more exactly centered on the scope to ensure a complete and clear image.