Pistol Construction Materials
By David Tong
The semi-automatic pistol market is possibly the firearms industry’s leading developmental focus. Having studied pistol construction for several decades, I have reached some conclusions about the plusses and minuses of each of the commonly used materials.
There are four concerns regarding the strength of materials commonly used in pistol construction. These are usually measured and quantified by the direction of the force applied to a given cross section (wall thickness) of a material. Compressive force is what the part mostly endures from recoil forces. Torsional strength is a twisting motion and can usually only be seen in ultra-high speed photography. Finally, tensile strength is a measurement of the ability of a part to resist stretching or shear forces.
Generally, the part is clamped into a machine with jaws that both hold and test the part. The yield point is the amount of stress that a material can withstand without permanent damage. Stress testing allows a manufacturer to test a sample of material in non-destructive as well as destructive ways. The information is usually quantified in pounds-per-square-inch.
The traditional material for firearms construction is high carbon, heat-treated steel. Generally, the Rockwell C scale quantifies the heat treatment runs and usually the frame is not as hard as the operating slide. These figures are approximately RC 30-40 for the frame and RC 40-55 for the slide, because the slide is the primary feed mechanism and serves as the locking abutment for the barrel.
Revolvers operate in compression as well. Recoil is absorbed by the recoil plate as the forces are applied to that part of the frame. Tensile strength is tested, as the frame is stretched by the same force on the top strap and crane areas, as well as pressure contained by the cylinder and barrel.
There is much to recommend steel construction. Steel’s properties are well known and the material itself is durable. While the material can be cast, forged, or fully machined from bar stock, economic production has become far less labor and time intensive due to computer controlled machining centers.
Steel’s strength also means that relatively thin structural cross sections can be used, compared to other popular materials, and this can play a role in ergonomic fit for people with small hands. Steel can be repaired by welding in some cases.
A working estimate of the strength of steel can be found in the larger “plastic range” than other materials. This means that it can operate reliably between a nominal yield point and the ultimate tensile failure point and endure deflection over a greater range of stress without damage. This figure can be as much as 40% of the difference between the yield and failure points. A decent hypothetical example would be a nominal yield point of 40,000 psi and a failure point of 65,000 psi. In other words, steel has a great capacity to absorb energy.
Major structures such as slides and frames can be made with castings, usually the lost wax or “investment” process. The much greater tensile strength of steel can make up for the amorphous grain structure that casting produces (compared to a forging), although a cast steel part is usually “over built” with thicker cross sections. This can be seen in the older Ruger P-series pistols that are somewhat bulkier than some other popular designs.
For smaller parts, the metal-injection-molding (MIM) process can accurately reproduce parts that require little or no finish machining. Most manufacturers, including those who advertise forged construction on major components, utilize MIM to control costs. MIM can create parts with very little shrinkage and high-dimensional accuracy. Good quality MIM parts can rival machined forgings for durability.
The weight of steel aids in control and aiming steadiness, although it makes carrying of the arm less comfortable. While advances in the design of mechanisms and understanding of recoil timing through computer aided design and high-speed photography provide advantages to lighter materials, there is no free lunch. An aluminum or plastic framed arm will always recoil more than equivalent steel ones, as mass times velocity equals energy whether delivered on target or absorbed by one’s hands.
Steel is easily finished. In the past, the standard finishes have been hot dipped bluing, nickel plating and manganese phosphate “Parkerizing.” Nickel plating is attractive and highly corrosion resistant, but not terribly durable. From the 1970's on, industrial chrome plating has been used to provide greater wear resistance and ease of cleaning, although it is not as corrosion resistant as many might believe.
Stainless steels offer inherent corrosion resistance. They generally have a lower carbon content to make them easier to machine and this can affect susceptibility to rusting. A more accurate description would be "rust resistant steel." A gunsmith I know once stated that most firearm-quality stainless steel tends to be somewhat “stringy” when machined. Stainless steel is harder on tooling and requires different cutting fluids than standard carbon steel, which increases production costs.
Automatic pistols made of stainless steel must have differential alloys and/or heat treatment for slide and receiver to avoid galling. The defunct firm Arcadia Machine and Tool used to make a 1911 clone with a very soft grade of stainless. This resulted in poor wear and galling of both slide and frame. Many revolvers have been manufactured of stainless and due to the softer metal alloys generally used, they can lose their cylinder timing under hard use faster, compared to standard carbon steel.
Various sprayed-on finishes, such as Brownell’s “Alumahide,” KG “Gun Kote”, Lauer’s “Dura Coat” and the newest process, “Ceracoat,” have been used on less aesthetically emphasized firearms. The latter incorporates a ceramic component that is head and shoulders more abrasion, corrosion and wear resistant than the others.
Steel’s drawbacks include its weight, its need for some lubrication and protection from corrosion and the issue of comfort at either end of the temperature range in which a firearm may be employed. I have always-preferred steel, believing its attributes outweigh its drawbacks.
Before World War II aluminum, though one of the most prevalent metals, was expensive to refine from raw ore and there was a traditional distaste for its use in firearms. The use of aluminum alloys was the industry’s first major post-war development for pistols, particularly for constant carry purposes. Colt introduced the Lightweight Commander in 1949, a slightly shortened and 30% lighter version of the Government Model, as an offshoot of the General Officer’s Pistol program of the era.
Weight is a big deal to a police officer. Burdened by a Sam Browne belt loaded with accessories that can weigh up to 20 pounds, pistols such as the Colt Commander, Smith & Wesson’s M39 automatic and M12 Airweight revolver lightened the load. An aluminum-framed arm can save between 35%-40% in weight compared to steel and that is important to someone who must pack the weight daily for long hours.
I do wonder how much this really matters to the civilian concealed carry permit holder when one’s pistol is carried in a well-fitting holster commensurate to your clothing and the weather. (Even more, because it is impractical for the civilian to wear a Sam Browne belt or a separate, wide gun belt to support a heavy pistol's weight. -Editor.)
I think it can be reliably stated that aluminum framed arms are not as durable as a steel one of equivalent design and cross section. There is no free lunch. Aluminum does not have the tensile strength of steel. The aluminum alloy must be carefully chosen and as much as 50% thicker in cross section, compared to an equivalent steel part. The cross section of a material becomes important to the pistol shooter, not only because of weight, but also due to ergonomic issues, such as balance and grip width. Aluminum is simply not as capable as steel of handling an auto’s slide recoiling into the frame. An aluminum revolver frame is less resistant to flame cutting and stretching than a steel one.
Aluminum has been a popular alternative to steel for the high-capacity 9mm pistol for decades. This use did have a gestation period, though. Carl Walther Waffenfabrik of Ulm, Germany, remade the P-38 pistol after WWII with an aluminum frame and these frames stress cracked far more frequently than the original steel design. Manufacturers must take into account the need for somewhat greater cross-sections in stress-bearing areas subject to recoil when using aluminum components.
The most prevalent surface finish used on aluminum has been some form of hard-anodizing process. Usually only a few mils in thickness, it offers greater corrosion and wear resistance and does not increase weight. The process can produce Rockwell C figures in the 60's on the wear surface of the metal. Usually the hard coat anodizing is applied over a glass bead blasted prepared surface. This produces a matte finish that is preferred for a non-reflective “social” pistol, although it does not have to be this way. A highly polished hard-anodized surface is possible, though rarer, mostly because of the additional labor costs involved in surface preparation. Aluminum can also be finished in decorative nickel and hard chrome, as well as the sprayed-on finishes mentioned above.
Drawbacks include greater felt recoil. Some aluminum alloys cannot be welded, including the “Coltalloy” used in the Commander. Repairs are generally not possible if fatigue cracks occur, although this also means that the expected life of the arm has been exceeded. Beretta claims on its website a 30,000 round life for its M9 service pistol. That is roughly one-third to one-half of the life of its steel framed predecessor.
The use of plastics in pistol construction was limited to non-structural items, such as grips and recoil spring guides, until the German firm of Heckler and Koch introduced the polymer framed Model VP-70 in the mid-1970s. While Steyr-Daimler-Puch of Austria made extensive use of polymer for the AUG assault rifle (including its entire trigger group!), the real revolution began with Gaston Glock’s seminal G17 of 1983. Not only did Glock use the material for the frame, he used it for a number of the smaller parts, as well. Anti-gun political zealots of the time attempted to argue that these plastic guns were not metal detectable in security areas. This was an outright lie, as all plastic pistols have a large steel component in other functioning parts. A Glock looks like, well, a Glock as seen on the screen of an airport X-ray machine.
Plastic components were adopted for multiple reasons. First, and most obvious, is weight savings.
Another is manufacturing economy. While the precision injection molds are expensive to produce, once done the molded parts are quickly and cheaply made. This is no small matter for any company concerned with cost savings on metal cutting equipment, legal liability expenses and profit per unit sold at normal retail levels.
Plastic frame construction has a third benefit, as the arms are very damage resistant due to compressive recoil impact. I have heard one anecdotal report of a range rental Glock 17 having shot over 350,000 rounds and Glock itself has one example that has fired in excess of a half-million rounds. There is no question that the material, at least in that company’s proprietary polymer blend, offers the prospect of generations of hard use capability that can be far beyond the expected life of more traditional construction materials.
Another big plus is the thermal neutrality of a plastic frame in one’s hand. Not having a very cold or very hot metal surface to hang onto means greater comfort over a much wider temperature range.
The plastic framed pistols that I have owned or tested all functioned reliably, were adequately accurate and were easy to maintain. Their very thin magazine wells allow for the use of large double-column magazines while maintaining a reasonable grip girth. Molded plastic can also allow for substantial ergonomic changes via the use of interchangeable grip panels to accommodate different hand sizes.
While these are all practical reasons for owning and using a plastic framed pistol, and I’d include the avant-garde mixed-construction Ruger LCR in this observation, they are the reasons why I admire them, rather than desire them.
As our esteemed Managing Editor, Chuck Hawks, has stated in these pages regarding plastic rifle stocks, polymer pistols engender little pride of ownership. I view them more as tools rather than “objets d’arte.” My conventional aesthetic sensibilities are offended by mould lines, plastic flash on edges and molded checkering or stippling.
Plastic offers far less tensile strength, making it more susceptible to catastrophic failure than either steel or aluminum. While over-pressure cartridges can damage steel or aluminum framed pistols, there are many more reports of polymer-framed pistols suffering explosive destruction, due to the material itself failing. These instances are relatively rare, considering the sheer number of polymer pistols sold, but the numbers are still significant. Arms manufacturers must take this into their economic calculus when considering legal costs against production savings.
Naturally, polymer’s very lightweight means that recoil control and aiming stability can be compromised, especially as the magazine runs dry. Though I have never fired one, I suspect that the .357 Magnum chambered version of the Ruger LCR, or the equivalent Smith & Wesson revolvers, would be distasteful to shoot. (David, you are a master of understatement! The LCR is "distasteful" to shoot with .38 +P loads. -Editor.) However, the Ruger LCR revolver is a masterpiece of mixed construction, combining all three of the major materials discussed in this article.
For many, plastic is the way to go as it offers corrosion proof construction, light weight, durability and lower acquisition cost when new. The hard-core Bauhausian “form follows function” adherent will discount or ignore aesthetic purity in his or her calculus. I hope that this short article will provide the reader with a balanced perspective for each material, based on the kind of usage one is considering.
Copyright 2011 by David Tong and/or chuckhawks.com. All rights reserved.