The Metallurgy of a Blade

This is a discussion for the ages… which steel makes the best knife?

If only there were one simple answer. It all depends on the burden of intended use, actual use, the frequency of use, and potential abuse one puts on a knife. As a basis for the argument, one must first identify the primary use of a knife. Then consider cost. Then maybe, future investment value as many high-end and custom blades appreciate better than most publicly traded stocks and commodities.

Let’s divide the field down the middle- a knife will either be used in a professional capacity or as casual every day carry, (EDC). The professional knife will be taken to task in the course of one’s job or duty. Or maybe remove a seatbelt from a victim of a motor vehicle accident. The professional knife may even see real violence if deployed in close hand-to-hand combat. The professional knife may very well be counted on to protect life, limb and freedom. Or maybe just to skin and dress wild game. The EDC knife, for casual daily carry, may be used to cut packaging or portion food, or may only ever be used as a letter opener. Though, at times the EDC pocket knife could be deployed to protect life and limb from an evil-doer. So the EDC knife may actually get to save the day.

The demands on one knife will never quite be the same as another. We can certainly make sound suppositions about what’s best. Modern technology has lent itself well to the advance of metallurgy to expand steel’s range of abilities. As diverse as modern steel selection is, they’re all very, very good materials. No steel of reputable pedigree should totally and completely disappoint. So even with the wide range of choice, most of our knife steels today will in fact perform satisfactorily, most of the time. Only when pushed to extreme limits will steel ever expose its shortcomings or strengths.

The steels listed and compared here all fall into the categories of Stainless, Carbon, or Tool steel. Stainless steel contains at least 13% chromium in the alloy content, and thus resists corrosion, but may sacrifice toughness at the lower end of the price scale. Tool steel can be very hard and offers the best in edge retention, but may sacrifice corrosion resistance and is more difficult (thus expensive) to craft. Carbon steel is tough, resilient, and easy to work with, but may totally give up on corrosion resistance.

Steel’s performance characteristics can be clearly defined, categorized and compared. Here on these pages are some terrific graphs from www.bestpocketknifetoday.com that display these characteristics in an orderly fashion. We thank Matt Davidson for his contribution to this issue and encourage our readers to visit his website. Edge retention, corrosion resistance, and material hardness are the most important factors in blade steel selection. First and foremost, a knife must cut. According to most serious enthusiasts, corrosion resistance can take a back seat to cutting power. Hardness, toughness, and edge make up the trifecta of a blade’s utility. A blade made from very hard steel is more expensive as it is more difficult to craft, and will be difficult to sharpen. In the case of economically priced blades, one that is easy to sharpen will be equally easy to dull; the compromise can go either way- cheap steel can be too soft or too hard. Either way, the edge will fail. Hard tool steel is more expensive but can be crafted into a thinner edge- which improves cutting power and eases re-sharpening. Only quality steel balances the properties of toughness and hardness to simultaneously resist fracture and deformation. Of course there are trade-offs and there are pay-offs to both economy and premium quality. But aye, there-in lies the rub. One must select a point of compromise. Even the most premium knife steels are not perfect. They always seem to give up a little to gain a little. To complicate matters, new materials are always being created to fill in small performance gaps.

As a guide to material selection, please allow us to make some rudimentary suggestions. Buy stainless or high grade tool steel for a pocket carry knife. Pocket carry knives will endure prolonged exposed to sweat and moisture. They need to be very corrosion resistant. Buy tool or carbon steel for a fighting knife. A weapon of this type may come to bear against an armed and determined foe. It needs to be imminently strong and sharp. Buy carbon or stainless steel for a hunting knife- just keep your carbon steel and tool steel blades clean and dry. If oxidation and corrosion can be kept at bay, you’ll appreciate the performance advantages carbon and tool steels afford over stainless. If attention cannot be given to blade maintenance, pick stainless. And if you choose stainless, carry sharpening equipment.

Another qualifying criteria- one that’s impossible to quantify in a graph would be value for cost. This is largely dependent on the brand of a knife, the steel of the blade, the sort of exotic materials included, and in the case of a handmade custom, the rarity or exclusivity attributed by the artist. Some brands sell quality. Some sell value. Some brands offer rare works of art that appreciate in value and mystique. Some brands sell pure hype and the promise that you will garner envy from your knife-collecting friends.. When studying the graphs, note that some steels may excel in one criterion, but lack in the other two (like 420 SS). These steels tend to be more economical, or suited to one application (420 makes a perfect fillet knife). Other steels that happen to hold their relative position in all three graphs (even if they’re in the middle), can be counted on to be great value for money (VG10, S30V, ATS34, 154CM). The rare few that hold their places at the high-end of hardness and edge retention (S90V, ZDP189, M390) can be expected to appear in pocket knives costing upwards of $400. At the very high end, many knife collectors will give up some corrosion resistance to get supreme cutting performance. One can care for a knife to prevent rust- but by will alone; one cannot make a blade tougher or last longer. It is demonstrably truer in knives than in most retail sectors; indeed, you stand a good chance of getting what you paid for. So it is with steel selection.

We thank Matt Davidson for his contribution to this issue and encourage our readers to visit his website: www.bestpocketknifetoday.com

By David Lake

Polymers and Composites

Drastic changes to tradition can be a hard sell- especially when that tradition finds deep roots in history and culture. If you’re reading this, then you are part of a very special culture- you’re a “gun guy”. And if you’re over 40, then you’ll recall the arrival of plastic pistols. You’ll recall the myths purveyed by the media and the doctrinal arguments hosted by the experts who either celebrate or condemn the idea of using plastic in the construction of a firearm. Despite early skepticism and trepidation, the merit of the concept has been well demonstrated, as now almost every small arms manufacturer offers a plastic gun. Hold-outs and traditionalists are hard-pressed to disprove the advantages in cost, weight, and resilience afforded by plastic.

Accurate terminology is important to this subject. When speaking of steel or aluminum, the generic names can be acceptably applied. Steel… is as strong as steel. And that’s enough. Or close enough as it makes little difference in idle conversation. Aluminum is understood to be very respectable stuff. Structures made of aluminum spend a lot of time performing extreme duties in exotic environments. However, when speaking of plastics and polymers and composites, one must use more specific designations, as all plastics are not created equal. In fact, the word “plastic” should be avoided, as it is not a correct descriptor designation of a type of material; it only refers to a distinct property of material. “Plastic” is not an adequate label for the superlative high-tech engineered materials used to replace steel and aluminum componentry in the firearms of today.

We should at least become familiar with the nature of a polymer. Poly means many; thereby a polymer is a compound built from many other compounds. Specifically, those compounds are called monomers and as it applies to this discussion, these monomers are formed from common hydrocarbons. Yes indeed, that means volatile gasses and liquids. As an example the basic hydrocarbon ethane can be made to repeat its base molecular structure- many thousands of times to form an enormous chain (speaking to the relative scale) that effectively entangles with neighboring molecules until the new material becomes a very strong solid. The common polymers are composed of very few elements; predominately carbon and hydrogen. We also find oxygen, chlorine, and nitrogen as small constituent parts of these compounds. There is a growing branch of material science that deals with something called a fluorocarbon. Fluorocarbons are manipulated to build fluoropolymers. These relatively new materials are still being discovered and explored. They promise strength and resistance that far exceed our current and common hydrocarbon polymers. These high-performance materials are the real future of polymer science. We should expect to see this stuff employed more and more in the near future. Hold your breath for the fluoropolymer pistol.

Material scientists can tailor a polymer’s properties to fill an exact requirement. If the material needs heat resistance, there’s a monomer structure for that. If a material needs increased elasticity, there’s a monomer for that. If a material needs resistance to stress fracture, there’s a monomer suited to impart that quality. The custom tailoring is performed by carefully manipulating of the way these elements combine. The subject may seem to be high science, and indeed it is, but the basic process can be well understood with the application of some Google. It’s an interesting field and its worth some study and familiarization.

Those gun companies that have ventured into non-metal construction have implemented technology beyond the basic polymer. These materials have been combined with small fibers or particulate of glass, carbon, or even certain minerals. Short fibers or particulate elements are evenly dispersed into a polymer to form a homogenous solid. This is known as “filled” polymer. This type of material generally does not give up any of the strengths and properties of the polymer to make room for the filler. The filler may be included to mitigate some inherent weakness or deficiency of the polymer. The filler may be used only to make the structure less dense, and thus, lighter. Most often, filling a polymer with an additive is done as a means to increase strength, hardness, or resilience. Sometimes polymers are filled with materials that have lubricating qualities to reduce operating friction on wear surfaces. Some polymer structures have even been infused with evenly distributed air bubbles to create structured rigid polymer foam. Though, not a filled polymer, the integration of air bubbles demonstrates how specifically these materials can be manipulated and improved. Filled polymers are cheaper to produce than machined metal, and are adequate for low to moderate load and wear surfaces. Polymer pistol frames are cast or molded into their final detailed form in a single step- a step that only takes a few seconds. This is the process used to create the frames of the HK, FN, Glock, XD and M&P pistols.

Though it was the first to claim broad commercial success, and still remains the front runner in the market, the Glock was not the first polymer framed pistol. Heckler and Koch released a polymer pistol almost 13 years before we ever heard of Glock. Almost 57 years ago, we saw the first rifle built on a polymer receiver- a .22 rifle from Remington. The proliferation of polymer framed firearms is proof that this technology is a good thing. The exact polymer recipes used by manufactures are tightly guarded industry secrets. Though, some authoritative independent research has been conducted to uncover the mystery of the exact composition of at least one of these guns. The Glock pistol frame is made of a type of nylon- that is easy to demonstrate. But even with the required lab equipment and some understanding of spectroscopy, we can only approximate the actual formula. Whatever be the details, we know that the Glock is a close cousin of stain-resistant carpet. The commercially present polymer that shares much with Glock DNA is called Nylon 6,6. We know that Glock has further manipulated the formula of Nylon 6,6 to increase its strength and hardness. Unique to Glock’s formula is an integrated fibrous, crystalline texture throughout the frame casting- though the Glock frame is not actually a “filled” polymer. The apparent fibrous structure is engineered into the polymer itself. Glock’s frame material makes a proud demonstration of our grasp and abilities in material sciences and engineering.

Given the similar requirements of all polymer pistol frames, we can assume that all firearm engineers have chosen similar polymer formulas. One feature common to all polymer framed pistols is the tendency of those frames to utilize an internal metal structure. Some feature a molded-in steel skeleton. Some just use removable metal structure that nests into the polymer frame. Both of these measures are affected to offer reinforcement at high-load and high wear areas. Filled polymers are found in long arms as well. Any designation of an item as “synthetic” usually refers to a rifle or shotgun stock that is made of a filled polymer. These materials are more resilient than wood- sometimes even considered indestructible. They are generally featured on entry level or “working” class rifles and shotguns. Long guns clad in polymer or synthetic furniture give up all points of luxury to remain totally utilitarian.

The other branch of non-metal construction involves layers of fabric woven from precisely oriented long fibers of glass, carbon, aramid, or spectra encapsulated and bonded by a polymer resin into a solid form. Aramid and spectra fiber are true polymers. Carbon fiber, though nearly 100% structured carbon atoms, begins life as a polymer film. The bonding or laminating resins used to encapsulate these fibers are also polymer, though of a special class. In theory, these thermosetting resins form one contiguous polymer molecule of the entire cured structure. The winning attribute of fiber materials like carbon and aramid is that they do not stretch- or they do, but very little. This means that a solid form made from these materials is very resistant to any change in shape. This type of structure, where linear fibers are encapsulated in a binder is known as “composite” structure. Composite manufacture boasts performance properties that far exceed the constituent parts. Though fiberglass had been popular and successfully used by gun manufacturers for many years, it has been outclassed by carbon fiber fabrication.

There are only two good reasons for carbon fiber’s popularity: it is impossibly strong and its visual appeal is timeless. As to the strength, it can bear loads and endure temperature fluctuation that could cause steel or aluminum to deform and fail. It nearly matches the strength of steel and aluminum at a fraction of the weight. This makes it good for shooter comfort. Its rigidity is far superior to that of steel and aluminum. It is less harmonic than most metals- that is, it does not propagate vibration. This is good for accuracy- as in repeatable and reliable day-to-day and shot-to-shot consistency. Composite manufacture, as it applies to gun manufacture, is usually used in high-power rifle stocks and barrels. The rifle stocks of McMillan and Manner’s are created using composite construction. The rifle barrels of Christensen Arms, Magnum and Proof Research marry carbon fiber with steel rifle barrels.

Composite construction is a very expensive and time-consuming method of construction. Complex machinery may be employed to wind fibers into a perfectly calculated pattern. Swatches of fabric are laid into a mold by hand to ensure proper alignment to achieve peak strength and beauty. Composite structures are cured for many hours under high pressure in massive ovens. Painstaking preparation, processing and finishing are required but the performance and appeal of the finished product is unmatched. The presence of bare carbon fiber garners envy at the gun range. The hypnotic weave of carbon textile or the random illusory texture of a filament wound structure adds a degree of interest and refinement to normally ordinary things. It’s inspiring and pride-inducing.

Healthy capitalism demands that all things meant to be sold should be accompanied by a fair supply of hype. The gun market is not immune to this tendency to exaggerate. Some manufacturers have labeled their filled polymer receivers “carbon fiber” and some even call simple plastics “high tech polymer.” All polymers are, generically speaking, forms of plastic, but all plastics are not polymers, and all polymers should not be considered high performance. A milk jug is made from polymer- with much science and study behind it. But it is neither high-tech nor high-performance by all standards. And when a manufacturer calls their product “carbon fiber”, it had better be made of laminated woven textile or filament wound. Both of these are easily identifiable by their unique appearance. A receiver made of an homogenous gray plastic is not carbon fiber- it is likely just a filled polymer. Even if carbon is used as filler, that material should not be described as carbon fiber. The consumer should be wary of fancy titles applied to the material from which a gun is made, and pay attention to the quality of what they can see and feel and know on their own. The overstatement of the facts is all too prevalent by advertisers­ and manufacturers. But we can also observe the modest understatement of facts as they apply to the capabilities and features of polymers. Most shooters don’t know that a Glock’s frame won’t melt until almost 500 degrees. Many shooters don’t believe that some polymer frames and stocks are totally chemical resistant- despite the existence of special cleaners made for “synthetic” firearms. Some just don’t believe the claims that the modern filament winding process used to replace some of the steel on rifle barrels, and the space-age resin used therein, can actually exceed steel’s tensile strength and heat-sinking abilities. Of course, this kind of peak performance asks that the barrel manufacturer exercise great care and attention to detail and perform exhaustive quality checks during and after manufacture. There are definite and distinct advantages to using new technologies in the gun market. Not all new trends should be immediately relegated as heresy. Excellence is possible, however not guaranteed when utilizing hi-tech materials. Be assured that there are indeed some promises and sales pitches that are simple farce.

One must not expect nor accept that a gun company can just replace some parts with carbon fiber or polymer structures thereby improving quality or performance of a gun. Any and all advantages afforded by the use of non-metals demand that the gun be re-engineered specifically to fully exploit a new material’s capabilities. Beware the polymer “version” of a pre-existing all-metal gun. One thing to be sure of, is that time will march on, and material science will open new possibilities. Guns will use metals less and less, and at the same time get stronger, lighter, and more efficient.

By David Lake

Aluminum

Second only to steel, aluminum is one of the most common metals used in construction, architecture, and general industry. The metal was first extracted from its ore in the first quarter of the 19th Century. 70 years would pass before aluminum alloy became economical enough to exploit its tremendous qualities of high strength and low weight. In its pure form, aluminum is soft and ductile- of little to no use as a structural material. It is highly reactive- that is, it easily interacts with and forms bonds with other materials. For this reason it is never found in nature in its pure form. Most commonly, aluminum ore presents as an oxide or silicate. In fact, aluminum is the most prevalent metal in the Earth’s crust. Aluminum can be recycled and repurposed indefinitely. If it can be said that the modern world is built on Steel- it must be said that the world moves forward on aluminum.

Everything that can be made of steel can be made of aluminum- by all modern standards and methods of manufacture and engineering. Aluminum can be formed and machined and otherwise worked as any other ductile metal can. The newest aluminum alloys claim a higher tensile strength than steel. There is even one particular type of aluminum that can best 6AL-4V titanium in most criteria- strength, weight, cost, and machinability. With all its boasting, Aluminum does fall short of other materials in some capacities. For starters, aluminum cannot offer the same resistance to heat as steel. High temp aluminum alloys exist, but they cannot approach steel’s 2500 degree melting temp. Aluminum enjoys only a relatively narrow temperature threshold where its strength and resilience remain useful (at the extremes of cold and hot, it becomes brittle and weak). And aluminum cannot endure the levels of abuse and mechanical stress that steel may take in stride. Aluminum tends to be slightly less forgiving than steel when pushed close to its limits of operational loads. It is indeed very strong per given mass- stronger than the same mass of steel. But while steel is tends to be elastic; aluminum behaves more like a plastic. That is, aluminum can be stressed only so far until it reaches its point of deformation- from where it cannot recover.

Aluminum only became a viable structural material post 1900. The early use of aluminum-copper alloy was seen in the frame construction of airships. Post World War I, heat resistant aluminum-nickel alloy would be utilized in the internal combustion engine and the (relative) high performance frames and engines of airplanes. Following WWII, aluminum alloy would be refined and specialized enough to find its way into jet engines. The aerospace industry would eventually become synonymous with aluminum- the terms “aluminum” and “aircraft alloy” would become generic synonyms. While the air and space industries do indeed employ aluminum structures, they clearly do not hold exclusive rights to the discovery or its purveyance. Be not be swayed by marketing strategies that use fancy descriptions like “aircraft aluminum” to sell a product. It is by common sense and logical conclusion that almost every industry has adopted aluminum to improve just about everything- gun manufacturers included. By 1949 Colt would announce a variant of the 1911 with an aluminum frame. Weight savings was the idea. Smith and Wesson would soon follow suit with semi-auto pistols and a few revolvers. Colt answered back with an aluminum snub-nosed wheel gun. Late in the 1950s, Europe would revisit its staple handgun designs with aluminum variants. While at the same time in America, some inspired aircraft engineers would put their heads together to create the AR-10. Some designs, as is the case with the AR-10 and AR-15, could only be possible with aluminum construction. Aluminum finds its purpose in firearm design right between steel and polymer. It matches the strength and approaches the durability of steel, while shedding much of the weight (lightweight is becoming more than a fad in small arms design). Hence the proliferation of polymer guns today. Aluminum is almost totally resistant to environmental and chemical attack- steel is not. And aluminum won’t distort or warp at elevated temperatures- which has been known to ruin a polymer-framed pistol.

As to the application of aluminum to the firearms industry, there is only one group of alloys- and within that, 3 “series” that will be encountered. That group is known as heat treatable aluminum. The alloys of direct interest and application to the gun industry will be any of these three series; 2000, 6000, and 7000. Each comes with its own set of benefits and deficits. Proper alloy selection should satisfy physical, chemical, and environmental requirements. Adverse operating forces and environmental factors encountered by a firearm are many. Most obvious would be the extreme pressures and stresses created by firing a cartridge. A gun’s mechanism may apply and divert and share and shed loads across multiple vectors and surfaces and structures within a single momentary stroke of the action. A firearm creates high heat and caustic or otherwise reactive byproducts during the ignition and combustion processes. A firearm requires routine cleaning and lubrication which means regular exposure to chemicals and substances. And a gun may be required to operate in extremes of temperature and humidity and salty or dusty and abrasive environments. One other noteworthy detail is the condition or temper of an alloy. This “T” designation describes the heat treatment and process a specific alloy has received. As the 4 digit alloy code describes the chemical makeup and suggests the general use, the letter code accurately describes that material’s specific capability. The most commonly known is T6. This heat treat condition can be applied to almost any 2000, 6000, or 7000 series alloy.

Heat treatable aluminum alloy can be manipulated or “tooled” by several means. A wrought solid (aka: billet) can be machined or cut into final form, or a final structure may be forged or drawn. A casting may also provide a lump of material that will need to be machined into tolerance. An exciting growing industry of “additive manufacture”, also known as 3D printing or (similar) laser sintering can also be used to form aluminum into a finished product. New material science and manufacturing processes are always evolving. Of interest is that one unique company is even using explosive energy (something close enough to RDX) to weld aluminum to steel substrate to create molecularly bonded dissimilar bi-metal pistol frames. One of the newest and greatest aluminum alloys known as Tennalum is stronger than most steels (in annealed state) and lighter than titanium of the same strength. Aluminum’s properties make possible certain structures and mechanisms that would be otherwise impossible. These miracles can be performed at reduced manufacturing expense compared to steel or titanium. Aluminum is easier to work and less taxing on manufacturing tools and equipment. Copper, manganese, silicon, zinc, magnesium, chromium, lithium, zirconium, iron, nickel, titanium and now scandium are all used to make specific aluminum alloys. Strength, hardness, elasticity, ductility, conductivity (both electrical and heat), and density are among the attributes that can be manipulated and prescribed to fulfill specific material requirements. The additive trace elements essentially imbue aluminum alloy with advantages over, and immunities from distinct physical, chemical and environmental influences.

One will likely not find an aluminum slide on a center-fire pistol. A slide contains locking lugs and other highly stressed structures. The receiver of a bolt action rifle should never be encountered in aluminum. A gun’s barrel must assuredly never be made from aluminum. And trigger parts can’t be made from aluminum either. It’s a great material- but it is a structural material. Aluminum cannot be expected (generally speaking) to repeatedly endure high wear or heavy impact. Aluminum pistol frames and AR-15 receivers house the internal workings and make interface with the locking surfaces and wear components. Pistol frames and AR-15 receivers are usually made from a 7000 series alloy- which can be as strong as some steels. These alloys can endure repeated light impacts, as is seen in the AR-15 buffer. If properly treated on its surface, or coated with a hard or lubricious coating, aluminum can ( to a degree) excel as a wear surface against opposing, moving components, as is seen in the lightweight and long wearing frames of Beretta, Sig, and some 1911 pistols. Alloys of a 2000 series designation match the strength of 7000 series; though the 2ks feature different alloying elements to adjust the metal’s chemical properties to meet more specialized applications.

The lesser alloy discussed here, known as 6000 series, are utilized in gun construction also. The fact that the material is not at the top of the list for achievement should not foster skepticism. Trust that any manufacturer has done the homework to make competent and confident decisions as to material selection. The performance of high-grade 7075 can in fact be matched by medium grade structural 6061- simply by the addition of more material. To reiterate, 6061 is not incapable of performing 7075’s job; it just takes more 6061 to do it. That should be acceptable to most of us who recreate with our guns on the weekends. There is only slight risk to accept when choosing a gun that includes 6000 series components. 6000 alloy might scratch, or dent with some entry-level abuse. Again, this should not give pause as most of us spend our own hard-earned dollars on our guns and intend to protect them from damage and abuse. Guns and components made of 6000 alloys might be identifiable by a thicker, heavier profile.

Once upon a time aluminum was in fact worth as much as gold. Today it is relatively cheap, but is used to make anything that must demonstrate a level of excellence. It is used as armor in vehicles and aircraft. It is used to form the structures of spacecraft; and also used as fuel to launch those spacecraft. Aluminum is diamagnetic; a property that makes aluminum the ideal material to be used as the “bullet” in next wave electro-magnetic artillery- called Railguns. And of course, the modern small arms industry we enjoy is only made possible by the judicious application of aluminum and progressive ideas of how to apply it to effect solutions to engineering problems. There is undoubtedly more new development to come. Years ago, the introduction of aluminum pistols and rifles garnered some enmity from the informed consumer. But science and experience healed that rash for most. Perhaps aluminum will usher in the day when steel is considered a substandard and inferior material from which we used to make guns.

By David Lake

Steel, Simplified.

Steel is the stuff of which the modern world is made. It is pervasive in history and its presence and application mirrors the rise and fall of man and his kingdoms as well as his proliferation around the globe. Scientists and engineers of the past century have been largely unsuccessful at creating its replacement. Barring the limitations imposed by the basic laws of physics, there are not many problems that cannot be solved by the judicious application of steel in one of its many forms. There is perhaps no better example of Mankind’s technological triumph than when he used steel to create the gun.

The oldest known “gun” by todays definition was developed in China (agree most anthropologists and archaeologists). The first guns created by the ancient Chinese were likely bamboo- or other hollowed out wooden tubes, which may not have been used to fire a projectile. There is some conjecture that these guns were first implemented as “shock and awe” technique- firing off bursts of flame and smoke to intimidate and confound a battlefield foe. It is unclear when exactly the gun would be used to fire a projectile- which was likely an accident the first time it happened. Man’s inherent need and ability to fix and improve things around him would ultimately adapt the simple pyrotechnic display into an implement crafted from steel, and intended to fire a projectile. The rest of the story of the gun follows man through the middle Ages, the time of exploration and conquest, and ultimately the industrialization and modernization of manufacturing and the globalization of commerce. There are marked times, usually times of war that spawned the great advancements in the science of the gun. Mounted cavalry, siege weapons, personal body armor, cannon and naval warfare all demanded that the gun become more potent and precise. Distance and accuracy and power would become requisite qualifications of the gun. Sometime in the last 500 years, the science of the gun seems to have reached a plateau, relatively speaking. Every shooter from a matchlock pistol to a shore gun battery would be made of steel (as they still are). Steel could provide the strength to exploit the power required to inflict the ranged effect we associate with the modern firearm.

The meter of the modern small arm often and deservedly defers to the “mil spec.” This is an established code of standardization. It envelops a set of rules and requirements for anything claiming to be up to par. It is not necessarily a qualifier of excellence or superiority- unless superiority can indeed be found in uniformity and consistency. The term “mil-spec” has become a generic descriptor, and is often applied to any of the wares and materials purveyed by today’s arms makers. And it is not entirely incorrect to refer to a steel alloy applied or used per an established mil-spec as “ordnance steel.” It is widely agreed that ordnance, or mil-spec steel refers to a specific family of steel alloy; chrome-moly, such as 4140. The enforcement of standards and uniformity is absolutely necessary to ensure any amount of quality and reliability in any system. Today all metal alloys are given a title or numerical designation from one of the authorities on metallurgy and engineering, the SAE, and AISI. These material names and designations describe a recipe or physical and chemical properties. So a steel may be described by what it actually is, as is the case with 4140CM steel, the 4 digit label indicates general type of alloy, and the precise levels of other additive elements to make the steel.

In actual terms, depending on the manufacturer of a gun or its components, the terms Mil spec and Ordnance Steel may be used to describe any of the following (but not limited to); 4130, 4140, 4145, 4150, 4320, or 4340 chrome moly alloys. The truth of the fact is that ANY steel may fall into the category of being “mil-Spec” provided that it satisfies the criteria set forth in the military standard for operating and yield strength for a specific application. There is a tendency for gun manufacturers to use misleading descriptions of their steel and its capabilities in order to promote sales. All steels are not created equal. This sales tactic can put the gun and its user at risk. All steels are not created equal; beware of the fly-by-night startup gun company that professes tactical supremacy but omits the metallurgical details of their operation. That said, modern firearms components from reputable sources (as are most things engineered) are designed with a “safety factor” in mind. Any gun barrel today should be designed with a minimum 1.5 safety factor- which means that barrel is designed to endure 1.5 times its intended operating load before failure or fatigue. The “mil-spec” for a steel structure usually demands a factor of only 1.5. Commercial engineering often requires a safety factor of 2.0 or higher. One should also be wary of the claim of “aerospace” in firearms design. The tolerance, safety factor and quality assurance by aerospace standards all become prohibitively expensive and ultimately restrictive to the end user. Aerospace grade demands a total detailed and documented control and trace of material from creation through use and operation. Nothing about your rifle is aerospace grade.

On to the specifics of the steel that may be encountered in the modern small-arm. There are only 4 general types of steel; carbon, tool, alloy, and stainless. All material that can be described as steel is one of these. The creators of steel add various trace elements to iron to achieve desired properties. All steel contains between .25% and 2.5% carbon, which allows the base iron to be chemically or thermally manipulated with or without the addition of other alloying elements. To earn the rank of stainless, the recipe of that steel must contain at least 11% chromium. Chrome moly alloy steel does contain chromium, but not enough to be stainless. And all stainless steel is not totally rust resistant. Some stainless is highly magnetic. It is doubtful that one will encounter a low carbon or plain carbon steel on a gun today; industry lawyers and a general concern for safety have well established a minimum for safety standards. Tool steel is capable of being very hard and tough, but is more difficult to craft. It may be used on guns in small amounts to form items like trigger parts or lock components. One should expect to find all (non-stainless) gun barrels and receivers to be made of an alloy steel; nickel-steel, nickel-chrome, or chrome-moly steel. These types of steel contain trace amounts- usually only up to 3% by mass of these other elements. The presence of nickel imparts extra strength and tremendous resistance to temperature and mechanical stresses. It is interesting to note that iron meteorites are usually an iron-nickel alloy- containing up to 25% nickel. That high nickel content is responsible for the meteorite’s ability to survive entry. The presence of chrome and molybdenum in steel alloy will increase hardness and resilience. Plain carbon steel is too weak and brittle or soft for firearms application. Chrome moly steels are not resistant to oxidation and other surface reactions to include rust and corrosion. Gun parts commercially produced from chrome moly steel are always encountered with a coating or treatment to inhibit surface corrosion. The most common are blueing and parkerizing which form protective oxide barriers on the steel. Chrome moly steel may be coated, clad, or plated in other metals like electroless nickel, hard chrome or newer high performance metal/polymer matrix coatings.

Chrome moly steel is indeed the first choice of the professional market. It is tough. It maintains strength and stability over a wide temperature range. It resists fatigue and failure caused by abrasion, wear and heat. Even in hostile maritime environments, today’s material science offers a host of treatments and coatings to protect the steel from surface attack. Chrome moly used in ordnance is not a “free machining alloy”, that is, it is difficult to machine and form. However, chrome moly does lend itself well to the application of these aforementioned coatings and surface treatments. We are all familiar with “chrome-lined” barrels. Most all gun barrels in general circulation with our armed forces- pistol and rifle alike are chrome lined (M-16 rifle, M9 sidearm). Adding a layer of abrasion and heat resistant hard chrome to the interior surface of a barrel adds longevity. In the case of the M16 or AR-15, if it is respected and not abused, a chrome-lined, chrome-moly steel barrel can expect to serve its owner with good function and acceptable accuracy up to or beyond twenty thousand rounds.

Stainless steel is rapidly becoming the default material used by barrel manufacturers. The most common alloy used in the gun market is known as 416R. This stainless steel makes an attractive barrel to be sure. It’s bright and shiny, and is known for being easy to machine. 416R is a “free machining alloy” which implies that it is created with a molecular structure that makes the material easy to cut. Free machining alloys employ trace amounts of lead and sulfur to improve machinability. While making this steel cost effective to manufacturers, and visually attractive to the consumer, the mechanical properties of free-machining alloy may also make it less desirable to the well-informed. 416R is not nearly as abrasion resistant as chrome-moly steel. And it can only claim 65,000 psi tensile strength (4140CM boasts 98,000psi). 416R does not resist fatigue and erosion from exposure to high heat. At high heat levels- those commonly encountered in military applications, 416 can distort, lose its heat treated state, and even de-alloy—a condition where the additive materials lose their microscopic bonds to the iron/carbon structure. So this material, while in use, could become unsuitable or even unsafe. Not to worry—416R comes with a reliable programmed response to imminent failure. It will split like a banana peel before it fragments. This splitting action is resultant of the “stringers” as they’re called, the areas of sulfur that co-mingle in-between the regions of martensite (crystalline structures) in the metal alloy. There are other grades of stainless one might encounter in barrel making. 410, 420 and 17-4 are less common, though they are found in use. 17-4 is renowned as a super alloy. It is fabled to get stronger from heat exposure. It has been said that it possesses mystical powers to “self-heal” micro fractures and surface defects. Few have ventured to deep-drill and cut rifling into a chunk of 17-4. Many have failed. The name Noveske will forever be remembered as one that succeeded. 17-4 is mainly used in pistol and revolver frames, muzzle devices, or small parts and even receivers and bolts of custom high-end high-power rifles. The last stainless worth mentioning here is 410 alloy. It is the underachiever of the bunch. The yield of this material is actually less than its intended operating threshold- a fact that some in the industry will argue. 30,000 PSI is where 410 can undergo “plastic deformation,” that is, be stressed past its ability to bounce back. Barrel makers still use this stuff knowing that a 5.56 NATO cartridge reaches over 60,000 psi just after ignition. Is this cause for alarm? Not really. Stress is calculated as a constant applied force. The pressure curve inside a gun barrel in not contained for any period of time, nor at a static load, but rather a burst that reaches a peak pressure. The pressure is not contained long enough or focused at a singular point where it could cause damage to the barrel. The barrel is saved by the fact that high pressure gas acts with equal force on all sides of its container (in this case the barrel)- and one side of the container (the bullet) is moving away from this applied force. So the bullet is effectively a valve that allows the pressure to escape. 410 alloy is said to be tougher and more abrasion resistant than 416. It is used by some manufactures to make gun barrels to save cost as it is imminently easy to machine. The more common stainless, 416R does deliver on some promises. Many custom rifle builders who work for the competition market trust 416R. Countless benchrest, palma and F-class records have been claimed by guns fitted with barrels made from 416R. This material does in fact make for a perfect surface finish during machining. This perfect surface lends itself to superb accuracy. A barrel properly ‘smithed from 416R will perform supremely, though not indefinitely. A match-grade stainless barrel fit to a high-powered competition rifle may be expected to have a good service life of 3000 rounds, more or less, depending somewhat on the caliber of the rifle, and largely on how it is cared for.

Steel of any alloy may be encountered in a number of “states.” This refers to the condition of heat treatment it may have received. Annealed steel has been softened. This condition does not imply that the steel is mild- only that it has been reduced to a softer state to make it more workable. Hardened steel generally refers to a surface hardening to improve that steel’s wear resistance or reduce its frictional coefficient. This condition may also be called “case” hardened. Heat treated steel is generally hardened throughout, also known as “core” hard. Core hard is a condition commonly employed on high wear or high load components. Certain alloys are better suited to be case hardened. Others are tailored for use in core hard applications. For example, the bolt carrier group in an AR-15 is made of several steel alloys- each selected for it properties as they fulfill the requirements of the BCG’s operation. The bolt itself may be made of something called Carpenter 158 that has been heat treated to a desired surface hardness to resist wear while maintaining internal elasticity, and resistance to fracture of the locking lugs. The bolt carrier body is commonly made of core hard 8620- a nickel-chrome-moly steel used for its superior resistance to heat induced fatigue and mechanical shock. The carrier houses a high-temp expansion chamber that is usually hard chrome plated. The gas key might be made of 4130CM, and specially coated to resist high temperature and impart lubricity so as not to cause abrasion to interacting surfaces. The cam pin receives tremendous abuse, and is formed from a core-hard piece of 4340CM—very high in nickel and chrome. The cam pin will endure severe abuse- repetitive compressive and shear forces and high heat imparted by the M-16’s operating system. These parts are often protected by a hard metal plating or clad in a metal/polymer matrix. Both, designed to kill friction and resist heat’s damaging effects.

So we can conclude that there is no “best” steel for your gun. Lesser materials may be used to great result provided proper engineering and quality assurance to back them up. Super alloys can lose all their attraction when cost and gained advantage are brought into proportion. Long past are the days of Damascus steel when one could be killed by his own gun if the bi-metal structure were to give way. The quality and consistency of steel used in the industry today exceeds the quality of manufacture implemented by the gun makers themselves. Our modern steel industry is nearly flawless. Good steel makes us better.