Adjusting the Tubegun Stock
by Germán A. Salazar
1. Stability: Prone is an inherently stable position because of the large amount of body contact with the ground as well as the low center of gravity. However, with a bit of attention to detail, a shooter can build a “more stable” prone position. A useful test of stability is to remove the trigger hand from the rifle while on aim - the rifle should not move at all. I do this as a natural point of aim check on each shot.
2. Durability: Once a string of fire starts, I will not remove the rifle from my shoulder barring unforseen or unusual circumstances (e.g. rifle malfunction). The simple reason is that I want to fire my 22 shots from one position, not from 22 positions. Therefore, the position has to be durable. Proper butt-plate and sling adjustments will keep the rifle firmly in the shoulder (without pain or discomfort) and proper cheekpiece height adjustments will keep your neck from straining. Ideally, your cheek should never leave the cheekpiece during the string (proper spotting scope adjustment is another topic, but obviously affects this point). Keeping the rifle in the shoulder for the whole string is a skill that takes some effort to develop; if you feel the need to remove the rifle for serious comfort or position deterioration reasons at some point in the string, do it. Minimizing change is the objective and two or three shoulder mounts are still better than 22.
3. Comfort: This element is often misunderstood; comfort does not mean you have the sensation of being in a recliner watching TV; it means you can get through 22 (or more) shots without pain. Your arm shouldn’t fall asleep, your fingers shouldn’t tingle, and your neck shouldn’t hurt. If you don’t have that degree of comfort you won’t have the durability we described earlier. Finding this comfort level is largely a function of rifle and sling adjustments and will take some time and effort.
Now that we have our objectives in mind, let's get to work on achieving them.
The first term we'll define is Length of Pull (LOP). Almost every piece of writing about stocks for over 100 years has defined LOP as the distance from the buttplate to the trigger - forget that definition. For our purposes, LOP is the straight-line distance from the buttplate to the pistol grip where your middle finger lies. Why are we changing a well established definition? Not to create confusion, but to define a dimension that actually means something in terms of the position. Suppose you have a trigger with an adjustable shoe, like an Anschütz or the CG X-Treme, if you move the shoe back and forth, have you changed your position? No - but under the old definition of LOP, the LOP has changed. We prefer to use LOP to refer to a dimension that will affect your position when changed. Look at the picture below, you will see that the LOP as we define it, on this rifle is right at 12 inches (draw an imaginary vertical line up the front of the pistol grip to the yardstick). All the pictures in this article can be clicked to enlarge a bit more.
Let's define a second term: Legth to Handstop (LTH). This dimension is the straight-line length from the buttplate to the front of the handstop right where the web of your hand makes contact. In the picture below, you will see that the LTH is 26 inches.
A third term that we'll define is Length to Sight (LTS). This is the straight-line length from the buttplate to the rear-most element of the rear sight. In the picture below you will see that the LTS is 14 inches.
In addition to those basic dimesions and terms, we'll work our way into some buttplate adjustments including cant, offset, buttplate height and cheekpiece height as well as handstop angle and handguard rotation.
Adjusting the stock is a process that you must work at and it builds on itself; as you get one adjustment right, the others begin to fall into place. Our hope is that you take from this article a system for adjusting the stock, not an exact set of dimensions; and that you understand that it will take continuous work over a period of time to really refine the adjustments. Your goal is not to obtain a "perfect set of dimensions" but rather a perfect feel that accomplishes the three objectives of stability, durability and comfort and the knowledge of how to change the adjustments to achieve those objectives under varying conditions such as sloped firing lines or other terrain features.
Adjusting Length of Pull - LOP
We begin our adjustments with LOP as it is a fundamental dimension.
- Adjust the buttplate so that there is no cant, no offset and the top of the buttplate is even with the cheekpiece.
- Remove the handstop and the rear sight. Make the initial adjustments holding the rifle in prone, with your coat on but no sling.
- Put a basic LOP on the stock. I'm 6 feet tall, the 12 inch length works well for me, add or subtract a little depending on your height (arm length, really, but they are related).
- The object of adjusting the LOP is to set the rifle up so that you are in the right place on the cheekpiece when in position. My definition of "the right place" is well forward on the cheekpiece. This means the loading port is closer to you and there is less of a reach to load while keeping the rifle in the shoulder. Additionally, a forward position keeps more of the rifle's weight between your hands, minimizing the dangle factor that causes fatigue during a long string of fire. A well balanced position is a real asset in prone shooting.
- The picture below shows where I have my face on the cheekpiece. With a Tubegun, the bolt slides underneath your face, so the old position constraint caused by the bolt running into the cheekpiece is no longer a factor. Get forward, you'll have a better balanced position.
I realize that not everyone is left-handed (only a few of us are so gifted), so here's a picture of John Lowther in position with his Tubegun. Looking at this picture I can see that John should probably shorten his LOP by about one to two inches. John has been shooting his Tubegun for about three months and is still working out all the adjustments but he's almost there. Compare the distance from the front of my cheek to the bolt handle versus John's. You can see he will have a longer reach to operate the bolt and to load the cartridge; that's not good. In fact, you can see the different angle on John's arm, that's the real problem, he's already stretched out and that's before reaching for the loading port.
At this point, you should have an LOP that places your cheek well forward on the cheekpiece, without going ahead of it - the cheekpiece must provide solid support for the head. If you have an older tubegun stock with the short cheekpiece and want to change, contact Gary for the new longer model. This first, rough adjustment should be done without a sling, handstop or rear sight. The reason we don't want the rear sight in place at this time is that its presence will cause you to move your head to create what you perceive as a correct distance from the sight. This will have an effect on your cheek placement that is artificial and will likely cause a poor position. The sight will be introduced into the system later in the process when the other elements are closer to finalized.
Adjusting Length to Handstop - LTH
Next let's move on to the LTH. Get the handstop out and slide it into the rail. Measure your LOP and make the LTH = (LOP x 2) + 1". You thought math class was out, didn't you? Well, that's not too tough, twice the LOP and one inch more. Again, this isn't a final adjustment, just a first pass at getting things set up. Try the position without a sling at first, it should allow a reasonably comfortable position with a 30 degree support arm angle.
The photo below shows Oliver Milanovic in position; Oliver is also fairly new to the Tubegun. Like John, Oliver is a bit too far back on the cheekpiece (needs a shorter LOP) but he has the older cheekpiece and is right at the end of it so he's doing all he can. Oliver's support arm is at a good angle to the ground, not too flat, not too high, and that indicates a good LTH. The reason we're looking for that roughly 30 degree angle is that it allows the sling to work properly, creating a triangular support structure with your forearm and upper arm that is very solid (like a roof truss) and will be the key element in maintaining a solid position through the string of fire.
The butt of the rifle should always be placed in the shoulder guided by your thumb at the top of the buttplate as shown below; this is the best way to ensure that it always goes to the very same place. Lifting it into the shoulder by using the pistol grip will never produce a consistent position, and if you are able to lift it in by the pistol grip, then the sling is very likely too loose. It should require a bit of effort to pop the buttplate into the shoulder (guided by the thumb) when the sling is properly adjusted. You should feel firm pressure on the shoulder and firm pressure on the web of the support hand.
At this point, you should have a reasonable LOP and LTH as well as a bit of offset and a reasonably well adjusted sling. If this is all done, you should be able to operate the bolt comfortably while keeping the rifle in your shoulder and you should also be able to reach the loading port to chamber a round without excessive movement. Loading from the shoulder will require some practice if you haven't done it before; there's a bit of ligament stretching involved initially, but it's worth the effort. Do your best to keep the rifle level while loading, remember that the objective is to minimize your movement and thus ensure that the buttplate remains in the same place throughout the string of fire. Your efforts to learn this procedure will pay off, don't give up on it.
Rear Sight Installation
You'll need a helper for this step. Get in position and close your eyes. Lift and lower your head onto the cheekpiece a few times while your helper watches. Ideally, your face is making contact in the same place each time and you aren't pulling your neck back or stretching forward too much; just a nice, natural, comfortable position. Once you have that established, close your eyes and have your helper put the rear sight and base onto the rifle so that the eyepiece is no more than 1.25" from your glasses. If your position and sling are well adjusted, that's enough to keep even a .30-06 from hitting you during recoil. If you look at the side view picture of me above you can see that there's only about 0.5" from the eyepiece to my glasses and that rifle is a .30-06 - good sling tension is the key to not getting hit. The closer the sight is to your eyeball, the smaller an aperture you can use in the rear sight which will sharpen the sight picture (this has nothing to do with the front aperture size, only the rear). Measure and record the LTS.
Record the LOP, LTH and LTS at this point, they will be useful references as the position and adjustments evolve.
Once the sight is in place, you can begin to adjust the cheekpiece height. Most people do this backwards and never get the full benefit of an adjustable cheekpiece; hopefully you won't be among them. Raise the cheekpiece until it is so high that you can't see through the sight. Now, while maintaining firm pressure on the cheekpiece with your cheek, slowly lower the cheekpiece until you just get to the point where you can see through the sight while maintaining that firm pressure. Later, as you begin to shoot the rifle and get the sights zeroed, you will repeat this exercise a few times, but remember to always start too high, not too low. The reason for starting high is to avoid the possibility that you are slightly raising your head to see through the sight as that would lead to inconsistent cheek pressure and thus a shifting point of impact. Consistency is the key to good scores, that's the same reason we go to the trouble to build a position that allows you to get through a string without removing the rifle from your shoulder - you want to fire 22 shots from one position, not from 22 positions.
After the cheekpiece adjustment, readjust the buttplate height to match the height of the cheekpiece. While you don't have to move it for every little cheekpiece adjustment, if you are making large changes in cheekpiece height, the buttplate should also be adjusted. Putting the top of the buttplate even with the top of the cheekpiece is a good place for prone; you may find greater comfort slightly higher or lower, but hopefully not too far from even.
Cant - the rotation of the buttplate on its axis - is often misadjusted or ignored. Cant and offset ar related but separate adjustments. In the past, when stocks were less adjustable, it was not uncommon to see shooters cant the rifle inboard in prone (tipping the top of the cheekpiece toward the centerline of the body). This was done in an effort to bring the sight more in line with the eye. However, there is a significant detriment to canting - the rear sight is no longer on a pure vertical axis, so when you make a sight adjustment it will have an effect on both windage and elevation - the point of impact will follow the exact axis of the sight. For that reason, we prefer to have the rifle in a pure vertical position and accomplish any needed rifle centering through the offset adjustment described above.
So, is the need for a cant adjustment dead? No, the cant adjustment is needed to eliminate cant! Once you are in your position and have developed it to the point of good stability, you may notice that the rifle has a tendency to cant; it may be an inboard or outboard cant. This is usually caused by the shoulder pocket being at an angle and the buttplate moving to settle into that angle. If you are fighting this tendency with the pistol grip hand, you are creating tension that will almost always result in increased horizontal dispersion of the shots. The correct solution is to slightly rotate the buttplate to eliminate the rifle's tendency to cant. On my rifle, for instance, I had a slight tendency towards outboard cant. I rotated the top of the buttplate slightly outboard, this allowed the rifle to remain vertical once the buttplate was placed in the shoulder, and that cured the cant. I will try to get a picture of this adjustment.
Some General Thoughts
The prone position should be one of solid control of the rifle. Your head should be over the cheekpiece, not on the side of the cheekpiece. The grip should be firm and the support arm at a 30 degree angle to create that roof truss support with the arm and sling. A position that's too low will do nothing for your stability; it will cause pain in the shoulder and forearm and will have referees and fellow competitors concerned over the rules compliance of the position. A position that's too high, with a very short LTH, will move the weight forward of the support hand, negatively impacting balance and stability. Like Goldilocks trying out everything in the Three Bears' house, we're looking for that "just right" balance of settings in our search for stability, durability and comfort.