Why Your Shotgun Stock Cracks and How to Avoid It
By Tom Brinson
If you have ever owned a shotgun or seen very many of them you are likely witness to cracked forearms and stock wrists in some older guns. There are a few simple reasons why this occurs and a few simple things you can do to prevent cracks.
Gunstocks have traditionally been made from walnut, with other woods substituted for economy in more modern manufacture and in military arms. Walnut is perhaps not the most ideal stock wood in terms of strength characteristics, but when its exceptional color, graining and weight is considered it has been the wood of choice for gun makers.
It is technically a hardwood, but is about the same density as most pines, very porous and tends to be a little brittle, but easily worked. Like all wood, it is a living thing that expands and contracts to the influence of its environment.
Wood, on a microscopic basis, is almost as much open space as solid, being something like thousands of tiny straws compressed together into a rigid longitudinal bundle. These straws or pores run in the direction of the grain, carrying moisture in and out of the piece as it breaths. Manufacturers cure their wood to a set of given conditions of resident humidity in the wood fibers and then form and fit the stock to the intended firearm. At that moment the fit is the best it will ever be.
Wood is stable in the direction of grain run, with insignificant changes in length due to its environment. However, it is unstable across the grain, expanding and contracting as moisture is transferred in and out, mostly through the open pores of end grain around the wrist, pistol grip and butt stock end.
Wood is weakest between the lines of grain, which is why cracks always propagate with the grain rather than across, except in a fracture. The finish you see on the outside of the wood enhances its beauty, protects the wood and seals it to retard dimensional changes, but few manufactures ever adequately seal the end grain, where wood movement is the greatest, in the inletted areas where the stock fixes to the receiver and under the butt plate. Movement at the connecting interface of stock to receiver is the primary point of most crack generation. Fractures can occur to stocks and forearms by almost any kind of accident because the wood at the wrist and particularly forearms are of small cross section. Accidents occur and are unpredictable but other cracks can be avoided with a little understanding of wood and attention to its needs.
Cracks in the forearms of pump, automatic and O/U shotguns are most directly linked to the wall thickness of these pieces and not so much the dynamics of wood movement. Some are reinforced by internal sleeves, but the wood pieces are still incredibly thin. Splinter forearms of SxS guns are hardier in thickness but are also subject to cracks in their thinner edges. To enhance crack resistance of these pieces, keep the mechanical fasteners tight that hold these pieces to their iron work. General use and the environment will tend to loosen these fasteners over time. Looseness will lead to cracks.
If a crack occurs in these thin pieces, no matter how insignificant, fix it promptly, as it will run. Where you can, remove the wood from its ironwork and coat the end grain and inner unsealed surfaces with several coats of linseed or Tung oil. These oils are easy to apply, are wood friendly and won't damage exterior finishes, but will seal the wood grain, making it more stable.
Mechanical fasteners are less likely to loosen if the wood isn't moving around them. Bedding a forearm iron to its wood on a SxS is a good way to avoid splits by taking some of the connecting load off the screws and spreading it more evenly over the wood piece.
Bedding is especially good to do if the piece had previously cracked and been repaired. If a forearm iron cannot be adequately tightened to the wood, the screw holes have likely begun to strip. An easy fix is to plug or fill the holes with epoxy and re-drill them.
The stock to receiver connection is the most critical, because shooting transfers recoil through the stock wrist and back toward the shooter's shoulder. This connection is a small surface area and point stresses can be high if the fit is not good.
Unlike rifles, with a single piece stock and multiple points of contact, shotgun stocks are always two pieces in breech loaders, regardless of action. When a shotgun left the factory, depending on the quality of manufacture, it was tightly fitted to its woodwork, but over time it will loosen with use and breathing of the wood.
Most shotgun stocks are connected to the receiver by way of a through bolt inserted through a hollow in the stock. This method leaves the greatest amount of wood in contact with the receiver and provides a sturdy connection.
Others, particularly double guns, may be connected by through bolts in the wrist. Some box locks, and worse yet side locks, leave very little thickness of wood to resist recoil stresses. If the connection was not good or becomes loose, even a little, it can lead to major cracks. Maintaining a tight fit is critical to avoid stress cracks in the wood and sealing the wood will avoid shrinkage and drying cracks.
A little regular attention can save you a world of grief and cost in repairing a stock. Here are some things you can do.
Remove the stock from your gun and inspect it for cracks. If there are serious cracks, have a gunsmith or qualified wood worker address them for you. Stopping a crack from running is far easier than repairing a completed crack. If there are no cracks, or if they are minor and tight, you may not need to address them further.
Inspect the stock to receiver interface to see how the stock bears against the metal. Hard bearing surface areas will be shiny. If the fit is good then these shiny spots will be well distributed across the surface. If the shiny spots appear concentrated in one or two spots you don't have a solid fit and there are high stress points of contact. The fit may have been less than perfect from outset, or because the stock had become loose for reasons already discussed.
A stock doesn't have to feel loose to be loose, as movement can be almost imperceptible to feel. No matter what the connection type there will be certain bearing points, some better designed than others, intended to transfer recoil shock into the stock. It is critical that as much of the receiver surface area as possible be in direct contact with as much of the stock as possible. A poorly fitted stock can be corrected by bedding the interface with an epoxy bedding compound to provide a snug, tight fit. On most shotguns that isn't too hard to do, but it may be something you want a gunsmith to do for you.
Do not file, sand or carve at imperfections in the wood interface, unless you are an accomplished stock fitter. You will likely only make matters worse.
Double guns, even those that have through bolts in the stock, have large areas of raw wood between the upper and lower tangs. Apply a few liberal coats of linseed or Tung oil to all the wood surfaces in these areas, especially the open pores of end grain. Be sure to do what bedding you intend before applying oil, as the epoxy will not stick to oiled surfaces. Wipe away any excess oil after it soaks in.
You may want to repeat this every few years. The point is to blind as many pores as possible to the transfer of moisture.
The butt area of a stock is most subject to cracks in the toe caused by impact, but because of the large surface of open grain is responsible for considerable moisture transfer. Remove the butt plate and apply a few liberal coats of linseed or Tung oil to the butt and as far down the bolt hole as you can get. Wipe away any excess after it soaks in and replace the butt plate. You may want to do this every few years.
Every season, or periodically if you shoot a lot, you should check the tightness of whatever fasteners were used on your shotgun; particularly in climates subject to considerable swings in temperature and humidity. Keeping this area tight and sealed against moisture change will go a long way in avoiding stock cracks in the wrist.
Not all gun makers are too diligent, for the sake of economy, about providing the best connection design and those guns may have a reputation for stock cracks. However, no matter how poor that connection design, following a few basic principles will help avoid cracking.
Copyright 2016 by Tom Brinson and/or chuckhawks.com. All rights reserved.