Taking Stock - part 2
In the last issue we covered the basics of gun stock design, nomenclature and composition. In this issue I'm going to introduce a few more terms and give you an overview of how these basic concepts apply to the stock on your air rifle and what you can do to improve the fit of your air rifle and hopefully improve your accuracy.
The law of averages - I'm going to start by telling you the stock on your air rifle was built to fit the average adult shooter. I call him Joe Average. He works for just about every air gun manufacturer. This means that the major dimensions of the stock were fashioned to fit a person that is 5' 6" to 5' 10" tall. Also a person that has average length arms, average length neck and face that's not too full in shape. If this description fits you to a "T" then you are in luck, you don't need the information contained in this tech article. If you're like me and not so average then read on. If you fall into the definition of non-average what you do when you shoot that stock designed for Joe Average is you compensate for the measurements that do not fit your body. If you are tall you bend your neck way over to gain a correct cheek placement. If you are shorter, you strain your neck to see the sights and struggle to reach the trigger because the buttstock is too long. All of these problems in stock fit lead to a loss in consistent accuracy. You need to be comfortable when you shoot. If the stock does not fit you, you won't be comfortable.
Length of Pull - The length of pull or LOP is measured from the forward face of the trigger to the end of the butt plate or butt pad. It should be measured to the point halfway between the heel (top) and the toe (bottom) of the butt plate. LOP is considered a very important measurement for any stock because the length of the buttstock will greatly affect how well you can hold your rifle and how well you will shoot. If the LOP is too short, you will tend to pull your shots to the right if you are a right-hand shooter. If the LOP is too long, the rifle will tend to ride upward and outward during recoil which will usually make you shoot low and to the left if you are a right-hand shooter. Reverse these directions if you are a left-hand shooter. For the air gun shooter, correct LOP can be determined by placing the buttstock along your forearm. Slip your trigger finger onto the trigger and the rest of your fingers around the pistol grip or wrist just like you would do if you were shouldering the rifle. Look down and see if the face of the butt plate or butt pad rests against your biceps. If it is just touching the surface of your biceps then the LOP is very close to being correct. You can further test for a correct LOP by shouldering the rifle and relaxing your right arm and letting your elbow drop as low as possible without being uncomfortable. Your elbow should be approximately in the centerline of the side of your body. If it's too far forward the LOP is too long. If it's too far rearward, the LOP is too short. These tests are just initial indicators of correct LOP. Because of variations in shooting styles you may still need to lengthen or shorten the buttstock to gain a correct fit. If you suspect the LOP is too short, you can experiment by using masking tape to affix pieces of 1/8" thick cardboard to the butt to see if this improves your hold. If the LOP is too long you can remove the butt plate or butt pad and see if this helps. Before cutting a buttstock to adjust LOP I would suggest referencing a few gunsmithing manuals to find out the correct tools for the job. Cutting a buttstock to shorten the LOP is not a difficult job but it does require specific tools and some specific knowledge on how to properly refit the butt plate so it will look correct. Whatever changes you make, remember to test them out thoroughly before making them permanent.
Drop - The amount of drop a stock has allows your head to fit the stock correctly. A stock needs some amount of angled drop along the top of the comb to allow the shooter to place his shooting eye directly in line with the centerline of the sights or scope. Since a scope will usually sit higher on top of the receiver than a set of open sights, the stock for scope sighted rifles should have less drop than a stock for a rifle equipped with open sights. Also the type of open sights will make a difference in the amount of drop that is required. Actually, drop is two different measurements, drop at comb and drop at heel. Technically, this measurement is taken by placing an imaginary line through the centerline of sight and measuring from the line to a point at the top of the front of the comb which is drop at comb; and a point at the top of the butt plate or heel which is drop at heel. Some people simply make this determination by placing a straight edge on top of the receiver and making the measurements. This is the simple way to do it but you need to take into account how far the sights or scope will sit above this line so you can make the necessary changes in comb height to allow for correct head placement. Most open sights require about 1/2" to 3/4" above drop at comb to be effective. Most scopes require about 1 1/2" of drop to fit correctly. Another aspect to take into account for finding the required amount of drop is the length of your neck. If you have a long neck you will need more drop, short neck, less drop. Also, if you don't want to scrunch your neck downward when switching between open sights and a scope, try to figure out how you will be using your air rifle the most and try to dedicate the rifle to just one type of sighting system. If you find you need more drop, the only way to achieve it is to shave some material off the top of the comb. You will want to start slow, don't remove more than 1/16" at a time. A sanding block with some 80 grit works well. Be sure to shoot your rifle after every alteration to check for proper fit and performance. The bare wood will have to be refinished after you are done. It's been my experience that most drop corrections can be achieved by removing stock material at the comb and not the heel. Start your changes at the comb and only move to the heel if it becomes absolutely necessary. Nowadays it is much easier to add a little more comb height than it used to be. Several companies offer strap-on nylon pads in different thicknesses that allow you to experiment with comb height without making any permanent alterations to your stock. There are also some stick-on, soft-rubber pads that will increase comb height. Check out our accessories relating to stock modifications on this page.
The Ideal - We get a lot of questions about how a stock should fit. The simple rule to remember is that it must be comfortable. What you want is a stock that you can pick up, close your eyes, shoulder the rifle, open your eyes and see the centerline of the sights or scope without having to adjust your body to fit the stock or move the rifle to fit your body. You should be able to relax and hold the rifle comfortably without straining. The more you have to adjust your body to fit the stock, the more you are working your muscles. The more you work your muscles the quicker you will fatigue. The faster you fatigue the sooner your shooting will start to deteriorate. It's that simple. Don't be afraid to experiment with fitting your stock. There are no rules to stock shape only the negative results of when it's the wrong shape and size.