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Gunsmithing Information

Scope Dope


by Les Bengtson


Every year, thousands of big game hunters take the field in pursuit of the elusive "trophy of a lifetime".  They spend hours carefully sighting in their rifles, days scouting out where the big bucks live or where the biggest bull elk will be during the brief hunting season.  Some will climb the high peaks in search of the elusive Bighorn sheep or the mountain goat. They might even travel to Africa or Asia in search of game.  This type of hunter takes his (or her) sport seriously.   They have the best equipment they can afford. Many hours are spent in deciding which is the best caliber for the game being sought.  More hours are spent deciding what is the best rifle to use. The time tested Model 70 Winchester?  The accurate Model 700 Remington?  The hard hitting Weatherbys?  Or a custom rifle on a Springfield or Mauser action?  One made especially to fit you with a Douglas barrel and a custom classic style stock?  What about Jeff Cooper's "Scout Rifle"?   Is this what is needed to take that buck that will put your name in the record books?  We spend hundreds of hours on planning every aspect of our hunting trips, but often spend only minutes on one of the most important aspects of our completed rifle -- the selection of its telescopic sight.


The selection of the telescopic sight for use on our hunting rifles is almost universal. As a working gunsmith, I even have customers bring in brush rifles like the 94 Winchester to have scopes mounted. I have also come to believe that the scope is one of the most important, and most overlooked, factors in a successful hunt. Two illustrations may help to show how the scope can have a significant impact on the hunts success.


One of my customers had a 94 Winchester given to him in return for some work he had done. He was very happy with it but was having difficulty getting the rifle properly sighted in with the iron sights. (They had been installed improperly at the factory.)   His solution was to have a scope put on the rifle. He selected a medium priced 3-9 power variable of the wide field type. His thinking was that the wide field of view would be useful for running shots in the brush. Unfortunately, he was not aware that when a scope is properly mounted on the 94 (except the angle eject models) you have to rotate the scope 90 degrees to the left to prevent the ejected shell from striking the adjustment turret. When mounted, the scope had a narrow field of view from side to side, but would be perfect for getting a full view of a giraffe. Additionally, by choosing a high power variable scope, he had turned his light, handy brush gun into an unwieldy club.


Another individual, hunting with me last year, was using a Remington 600 carbine in .308. This was a superb rifle for the mixture of open forest and brushy canyons found on the Kaibab plateau of northern Arizona. To keep the rifle compact and easy to handle, he had selected a Burris Mini-4X scope. Unfortunately, this scope has a long eyepiece lens assembly which, combined with a short length of pull on the stock, caused him to miss several deer due to the scope "blacking out" when thrown quickly to the shoulder for a snap shot.


From the foregoing examples, we can see that there are four variables affecting the proper selection of a telescopic sight for use on our hunting rifles. They are: Power of the scope, the size of the objective lens assembly, eye relief, and length of pull of the rifle stock. The last three are interrelated and explain why a scope that is perfect for one rifle may be next to useless on another.


SCOPE POWER

A telescopic sight does little to affect the accuracy of a rifle. (Townsend Whelen wrote that a scope is capable of one inch accuracy at 100 yards divided by its magnification. This means that a 4X scope is capable of holding aiming error to 1/4" at that range. Most people cannot see increments this small at that range. The difference between a 4X scope and a 2X scope at normal hunting ranges is insignificant.) A scope lets us see our target much more clearly and puts the sight and target in the same focal plane. The more powerful scope also tends to magnify the movement of the rifle, especially when fired under hunting conditions--often off-hand and out of breath. The high power scope that is rock steady off the bench rest wanders all over the target when fired at a deer from offhand. The most commonly recommended scope for the "average" hunter is the 4X. I feel that a good quality scope of 2-3X is more suited to the average hunter. The scope does not exaggerate the rifle's movement as much, is more compact, and normally weighs slightly less. All of these factors can be significant after a long walk up and down hills. The 4X scope becomes a decided benefit when the shots are normally taken ranges over 200 yards or when you normally shoot from a more solid position. The 6X scope is useful for shots normally taken at very long range such as sheep or antelope. Variable power scopes offer the advantage of being able to pick your magnification at the expense of being bigger, heavier and somewhat more fragile. I used one while hunting in Germany where the hunting conditions are very controlled and you normally shoot from a platform providing a solid rest.


Whichever scope is chosen, it should be compact, light weight and strong.  Quality is important and expensive, but in the long run, the purchase of a lower power, higher quality scope will prove more cost effective than that cheap variable that was on sale at the local discount house.


EYE RELIEF

Every scope has a point at which the full field of view is obtained. This is called eye relief and is normally expressed in inches from the rear of the objective lens to the eye. Most of today's scopes have a "critical" eye relief. That is the eye must be located at an exact point or you tend to get some blacking out of the field of view. Many older scopes had a "non- critical" eye relief that allowed between 1 1/2" to 2" of tolerance in eye placement. This critical eye relief is why my hunting companion kept having his scope black out on him. The scope could not be mounted far enough forward on his rifle to give him a full field of view unless he pulled his head back farther than normal after shouldering his rifle. Eye relief is built into the scope and cannot be adjusted by the user. The positioning of the scope in the mounts, can be adjusted and the scope moved to obtain proper eye relief. One of the most significant factors in how far the scope can be moved forward is the length of the eye piece assembly.


EYE PIECE ASSEMBLY

The eye piece assembly consists of the rear lens cluster, the threaded portion of the rear scope tube and the lock ring that locks the rear lens cluster securely to the tube after the scope has been focused. This length controls how far the scope can be moved forward in its rings when adjusting the scope for proper eye relief. Sometimes, this assembly is so long that the proper eye relief cannot be obtained without going to special bases or rings.


LENGTH OF PULL

While not usually thought of as one of the factors in selection of a scope, this is a prime factor in the operation of the rifle system that the scope is attached to. The length of pull on a rifle stock is the distance from the front of the center of the trigger to the rear of the center of the butt. The "average" length of pull is 13 1/2", but can vary from 13 - 14 1/2". Sometimes an individual will decide that he needs a recoil pad on his rifle. He will remove the old butt plate and then screw on a recoil pad and sand it down to fit the contours of the stock. When this happens without shortening the stock, the length of pull is increased. If the rifle fit the shooter before, it will not now. Additionally, if the eye relief of the scope was correct before, it is probably not correct now. Proper length of pull differs for each individual, although most can use the standard 13 1/2" fairly well. It also differs with the amount of clothing worn when shooting. A rifle that fits perfectly when shot during the summer in a light shirt would be too long when used with heavy winter clothing. A rifle set up for winter would probably be too short when fired in summer. But, length of pull is critical to the placement of the cheek on the stock and controls whether the eye will be properly positioned in relation to the scope.


There are four ways of handling this situation. The first (probably the most common) is to only shoot your rifle during hunting season. The second is to have one rifle for use in summer and another, similar, rifle for use when hunting big game. A pair of rifles, one in .223 and another in 30-06 having the same scopes, the same type stocks, etc. is another common solution. The third solution is to set the rifle up for winter use and to use a slip on type recoil pad during the summer. The last solution is to get two recoil pads fitted to the rifle. One a thin pad for use in the winter and the other a thicker pad for installation in the summer. Regardless of the solution chosen, the objective is to keep the face positioned at the same point under all conditions. Only after this is accomplished can we begin to deal with the variables of eye relief and eye piece assembly length.


SCOPING THE RIFLE

After we have stabilized the face's position on the stock through length of pull, we can begin to choose the proper scope and adjust it for proper eye relief. While having the face in the exact same position each time may seem like a small point, I have found that differences as small as 1/4" in face placement may be significant. A 1/2" difference can be enough to cause you to miss a shot.


The first thing to do is to decide on what type of scope you want- a fixed or variable. Then decide on the power or power range to be used. After this is decided, begin to look at the different brands of scopes to see which has the combination of eye relief and eye piece assembly length best suited for use on your rifle. The best way to do this is to mount the bases (if required) and scope rings on your rifle. Then mount the rifle to your shoulder wearing the same clothes you would be wearing when hunting. Have a friend measure the distance from the back of the rear scope ring to your eye. Do this several times and take an average of the measurements. This measurement will allow you to figure whether a particular scope will work on that rifle with the rings you are using. Assume that this measurement is 7". If the eye piece assembly of the scope you are considering is 2.9" long, you can use a scope having up to a 4.1" eye relief. If, however, the distance from the back of the ring to the eye is 6", that same scope would require an eye relief of 3.1" or less. Using this measurement, you can examine the available scopes that meet your specifications and determine the combination that will work for your particular situation. But what if you cannot come up with a combination that fits?


This is unlikely, but has happened to me several times when setting up customers' rifles. It most frequently occurs when they have already bought the scope and bring it in for installation and bore sighting. In this case there are several options. Another base may be used that will position the scope farther forward. I once obtained more distance on a Remington .22 by swapping the bases front to back. Two piece bases, such as the Weaver often have the cross slot for the rings cut nearer one end of the base than the other. Small adjustments may be made by turning the base around. This gives an additional bit of eye relief. The other alternative is extension rings that move either the front or rear ring farther forward. Sometimes a combination of these efforts may be required.


MOUNTING THE SCOPE

The bases should be securely mounted to the receiver and the screws secured with either Loc-tite or epoxy. While it may seem like I am trying to drum up business for gunsmiths by suggesting that you have a qualified one install the scope, I have seen even factory drilled and tapped rifles that required shimming to properly fit the bases to the rifle. There are tolerances in both the manufacture of the rifle and the bases that almost guarantee that they will not fit perfectly. When this happens, the scope may be bent slightly when installed. In one case I examined, the scope was bent to the point that it could not be properly adjusted.


Next, the rings should be installed and the scope positioned loosely in them as far forward as possible. (It should, however, take a bit of force to move the scope. You do not want it to flop around during the adjustment procedure) You should then mount the rifle to your shoulder and have a friend, or your gunsmith, move the scope back just to the point that you get a full field of view. Make a small alignment mark on the scope where it comes in contact with the rear of the ring. Then adjust the scope until the crosshairs appear straight up and down. This normally varies slightly with each individual. Then drop into the sitting position and see if you still have a full field of view. If you expect to use the rifle from prone, use that position instead of sitting. When standing, the head is farther back on the stock then in other positions. As you get lower to the ground, the head tends to move forward on the stock. This is why you adjust the scope backwards until it just comes into full field of view from the standing position. There is normally enough tolerance in the eye relief to allow a full field of view in the lower positions. If, however, you cannot get a full field of view in the lower positions, extension rings are indicated. Finally, tighten down the screws securing the scope to the rings securely, making sure not to cause the crosshairs to shift to one side. Most gunsmiths do not secure the screws in the rings with epoxy or loc-tite, but some do. On a rifle that is to see hard use, it might be advisable to use the blue Loc-tite since these screws can loosen and cause the point of impact to shift. Jack O'Connor once noted that during an African safari every one of the 14 screws on his scope bases and rings became loose and caused shifts in the point of impact. If I were going on an a hunting trip longer than the normal "deer season" type, or if I were flying to Alaska, Canada or Wyoming for that "trophy of a lifetime", I would lock-tite the ring screws.


As can be seen from the foregoing, there is a lot more to scope selection than just going out and buying whichever scope is on sale and mounting it. Considering the importance of a good sighting system and its relatively low cost as compared to most other aspects of a hunting trip, the small amount of time and effort put into selecting the proper scope and mounting it securely is cheap insurance that will help put meat on the table or a trophy on the wall.


This monograph may be reproduced only for non-commercial use without other permission of the author. Reproduction for commercial use only by written permission.


Copyright © 1999 by Les Bengtson