LOCK, STOCK, AND BARREL: Building a Better Rifle
Shooting is all about hitting the target with accuracy and efficiency -- not to mention having the best, most durable and advanced rifle possible. Here are a few things that make a rifle the lethal weapon that it is.
Staring Contest: A Marines Corps small arms instructor and his M-16 rifle. (Photo by Cpl. Sandra Zarate, USMC)
One well-aimed shot could do the job, especially if the shot is from the hands of an expert marksman or sniper. Unfortunately, not everyone can destroy targets at extended ranges while wasting only a few rounds. Skill plays a large part in accurate and effective shooting, but without a dependable rifle, it would be like Springsteen playing some rinky-dink $50 guitar. Some say it's the singer not the song, and it would follow that any master marksman could transfer his sharp shooting skills to any firearm. But when it comes to rifles, there are a few details that could make all the difference, and are well worth splurging on.
User Interface
The quality of a rifle is dependent on several different features -- stock, action, trigger and barrel. The stock is the "user interface" -- the surface that the shooter grips and maneuvers in order to aim the rifle. Stocks come in many shapes and sizes, but the most important quality is what they're made of. Most types are made out of any of three different materials -- wood, wood laminate, and synthetic.
Wooden stocks are manufactured from a solid wood blank and most commonly use walnut, or some other type of hardwood. The only requirement as far as wood choice is the wood's ability to handle the recoil -- there are few, if any, balsa wood stocks on the market. Hardwood stocks are heavy, less flexible when fired, and can put up with a large amount of recoil. While they are not as customizable as synthetic stocks, and are more susceptible to environmental conditions (moisture and temperature can cause wooden stocks to warp) wood stocks are reliable and sturdy, the choice of many of our forefathers.
On the other side of the spectrum is the synthetic stock. These are non-organic and sometimes exotic compounds such as carbon fiber or Kevlar. Most are made from either fiberglass or injection molded plastic. Synthetic stocks are obviously lighter than their wooden counterparts, which comes with a few drawbacks. First, they absorb less recoil. Second, they are significantly more flexible than wooden stocks, as a result of being fired as well as side stress caused by carrying slings. To remedy these two flaws, a rigid metal bar, called a bedding block can be installed into the stock, adding more weight and stiffening its structure. What are the advantages, you ask? Most importantly, they're cheap and easy to manufacture. In addition, they require such little maintenance, they can be molded and stored for years without a problem. Lastly, for the style-savvy, synthetic stocks come in a myriad of colors -- for camouflaging or matching your favorite outfit.
Wood laminate combines the best of both worlds, taking the most useful qualities from wood and synthetic materials. Wood laminate isn't quite wood, but isn't quite synthetic either. It consists of a number of wooden strips glued together under pressure, and then machined into a stock blank. Laminated stocks absorb recoil like their wooden predecessors, and are more stable firing platforms than synthetic stocks. During assembly, the wood grain of the various layers of the laminate is aligned in a cross-pattern, stiffening and strengthening the stock. This eliminates the tendency of warping. The gluing process also treats the wood, making wooden laminate stocks even more impervious to the elements as synthetic. Synthetic, however, is the stock of choice for the military because of their adaptability and battlefield durability.
Different barrel and action combinations of the M40 Sniper Rifle (Image from Remington website).
In the Action
All weapons have an "action." This refers to all of the parts necessary to chamber and fire a projectile. Actions are characterized by their method of operation -- manual actions require the shooter to manually operate the action, whereas automatic actions perform this autonomously, usually through recoil force or trapped gas.
There are a number of manual action rifles, from "dropping breech" and "lever action" to "break open," among others. Most common by far is the "bolt" action. Bolt-action rifles get their name from the manually-operated bolt they use. Once a weapon is fired, the shooter manually unlocks the bolt and pulls it to the rear of the action. This not only extracts and ejects the spent cartridge case, but also re-cocks the trigger for the next shot. After the bolt is pulled to the rear, it gets pushed forward again, locking it and stripping the next round out of the magazine. The round is then seated and chambered, ready to go.
Bolt-action rifles highly accurate and efficient for the simple fact that the entire weapon-action, barrel and stock acts as a solid mass. When the gun goes off, there are no moving parts, allowing for precise and predictable shooting. One downside is that bolt-action rifles are very slow when compared to automatic rifles, and do not have large magazines, with capacities that range from 5-10 rounds.
Automatic actions cycle between shots automatically, either from the recoiling effect from the fired bullet (the bolt is physically pushed backwards) or via trapped gas (compressed chamber gas is bled off into a mechanism that converts this pressure into physical energy). While such weapons are capable of high degrees of accuracy, such as the M-14, they are not nearly as accurate as a bolt action rifles because of the amount of moving parts. This makes for inconsistent round to round firing conditions. On the other hand, what the automatic rifle lacks in overall accuracy, it makes up for in volume of fire. All modern combat rifles utilize some form of automatic action, which also facilitates the use of large capacity (30+ rounds!) detachable magazines.
Smoking Barrels
Arguably the most distinctive feature of a rifle is its barrel. Like stocks, you have your choice of various materials. The most common are stainless steel, chrome moly, or chrome-lined steel.
Stainless steel barrels are made, as one would think, from stainless steel. This isn't your run-of-the-mill cutlery-type stainless steel, but rather a steel alloy with very high chrome content. These barrels are the hardest of the bunch, so they offer the highest degree of accuracy and life. Unfortunately, because of their high chrome content they are difficult to blacken -- shiny barrels are a bad thing in the Army -- and so are often only used in civilian applications.
Chrome-moly barrels are barrels made from a steel alloy containing chromium and molybdenum. They have the advantage of having good accuracy and durability, and are significantly cheaper than stainless steel barrels.
Finally, we have chrome-lined steel. These barrels are those made from a steel alloy that is subsequently lined with chrome to improve the corrosion resistance of the barrel. Because it is only the interior of the barrel that is chromed, the exterior can be treated to meet any specification. Chrome-lined steel is the barrel material of choice for the military because it is cheap, has good corrosion resistance, and perhaps most importantly, isn't shiny.
Other Barrel Options
Lapping is the process whereby an abrasive coated led plug (the lap) is pushed through a barrel. Lapping a barrel removes any machining imperfections left in the barrel, and barrels can be lapped several times during their construction process -- during the initial boring, the subsequent reaming, after the rifling is cut, after the chrome lining is applied. While lapping is used extensively in custom-made barrels, its use in military firearms is limited to purpose built sniper rifles.
Bull barrels are barrels that have significantly more mass than more conventional or "sporter" barrels. The purpose of this additional mass is to act as a "heat sink" by absorbing the radiant energy associated with firing. As a rifle is fired, the heat from the propellant gasses is transferred to the barrel. As barrels heat up they are subject to warping. The greater mass of the "bull" barrel allows more energy to be absorbed before barrel warping occurs. The down side, however, is that bull barrels are much heavier than conventional barrels, which precludes their use in common battle rifles, where weight is a limiting factor.
Custom Features
There are a few other extras aside from your basics like stock, action and barrel that can make shooting even more efficient and precise. "Floating" or "bedding" barrels can ease wear and tear, while two-stage triggers can make for cleaner shots.
A Marine aiming during sniper training. (Photo by Lance Cpl. K.T. Tran)
Firing bullet after bullet is sure to generate a lot of heat. This can cause the barrel to expand and warp due to uneven pressure caused by imperfections in the stock. One way of eliminating this harmful pressure is to "float" the barrel. That way, when the barrel heats up, it literally "floats" in air, and will have nothing pushing against it.
Another way to mitigate the pressure caused by heating up is "bedding" the barrel. Bedding is essentially the opposite of floating. When an action is "bedded" it is pressed into a moldable compound (typically fiberglass or epoxy) to achieve a uniform and durable "bed" upon which the action can be bolted. Bedding can be either full or partial. A partial bed supports only a small portion of the action, usually only the first 3-6 inches forward of the chamber, leaving the rest "floated." A full bed supports the barrel through the entire length of the stock. Pillar bedding is when a number of machined metal "pillars" are attached to the rifle's action and are incorporated into the bedding process. These pillars establish a permanent, non-compressible metal-to-metal reference point for the action, which eliminates the variable stress loading that comes with the more conventional metal to wood bond. In block bedding a metal sleeve (either steel or aluminum) is permanently attached to the barrel and then bedded to the stock. The advantage here is that with the exception of the bedding block, all of the rifle components are free floating and under no influence from the stock.
Two-stage triggers have two distinct stages, the "take up" stage, and the "break" stage. The purpose here is to introduce a certain amount of play in the trigger, enabling the shooter to engage and squeeze the trigger the same way every time. This is accomplished by having two different springs of different lengths and pull weights. The first stage will typically have a pull of 3-4 pounds, while the second stage will only require a pound or two more. This allows the shooter to take up a good sight picture, take in the trigger slack, and fire a clean shot when ready.
"To secure the peace is to prepare for war." George Washington and later Metallica.
