The History of Stamping Steel for Mass Production Firearms

There is a timeless allegory concerning a boiled frog. I know you’ve heard it. Though I’ve certainly never tried this myself, legend has it that dropping a live frog into hot water results in some frenetic efforts on the part of the amphibian to extricate himself. Purportedly the best way to boil a frog, should you ever wish to do so, is to put him in a pot of cool water and then increase the heat slowly. He will therefore supposedly bask about in the warmth right up until it is too late to react to his dire circumstances.

The classic application of this odd truism is in tolerating deleterious social change. Shocking, radical, transformational cultural changes often result in revolution and violence. However, the same stuff gradually massaged over time can metamorphose a society without anyone’s being the wiser. Sometimes the most momentous events can be lost in the background clutter as a result.

I cannot fathom ever having need of boiling frogs myself. However, as it applies to our discussion today, I would posit that the world has been radically changing around us and we honestly haven’t much noticed it. With familiarity inevitably comes complacency. As regards modern technology, the curve has of late become asymptotic. This simply means that technological advancement is building in an exponential fashion. It is not simply that science is advancing linearly, such stuff is veritably exploding. While consumer electronics represent the most obvious example, you can see this in weapons design as well. The current rarefied state of the art really began with the Industrial Revolution.

The Chinese Type 56 SKS is a great stamped-steel rifle. Learn more about the SKS here

Origin Story

Historians place the onset of the Industrial Evolution around 1760. Prior to that time if you wanted a product some poor slob had to squat down in the dirt and make it by hand. Thanks to the innovations surrounding automated textile manufacture, steam power, advanced iron making techniques, and the development of machine tools, smaller numbers of workers could produce larger numbers of higher quality products. In short, at the beginning of the Industrial Revolution mankind began using more brains and less hands.

In the world of gun making, this eventually meant standardized parts. We take that for granted these days. If you get a milspec AR parts kit you can rightfully expect all the holes to line up and the sundry components to work without too much fuss. Such was certainly not always the case. The British Land Pattern Musket was first designed in 1722. 4.3 million copies saw service. The Brits affectionately referred to the thing as the Brown Bess. The etymology of the term likely arose as a veiled reference to the prostitutes of the day. Brown meant drab, while Bess was a generic moniker used to address a lowly woman.

Despite such a massive production run (by comparison, we only made 1.5 million Thompson submachine guns in total during WW2), the internal parts of these muskets were all made slightly oversized. Final production involved hand fitting the lock work to ensure smooth, reliable operation. However, in 1798, a contract was let to Eli Whitney, the inventor of the cotton gin, for 12,000 muskets for use by the Continental Army under President George Washington. Whitney’s 12,000 “smoke poles” were supposed to utilize interchangeable parts. One hammer, trigger, or sear should be a drop-in fit on any of the other 12,000 weapons. With that the whole world moved just a little bit.

Now fast forward to World War 1 and you have the planet’s first global conflict on a truly industrial scale. Massive factories produced war materiel in volumes previously unimagined. This fact combined with the widespread use of smokeless powder, high explosives, internal combustion engines, and such diabolical stuff as poison gas transformed the way men killed each other. However, throughout it all, most small arms were still cut from big pieces of forged steel one component at a time.

A cursory study of the major weapons of the day makes this obvious. Guns like the P08 Parabellum Luger, the M1911 pistol, and the Browning Automatic Rifle all started as big billets of forged steel. Like Michelangelo’s David, the machine operator then simply removed everything that wasn’t a gun receiver. What’s left is a sort of mechanical objet d’art. This technique makes superb reliable weapons, but it is time consuming and tedious. Nowadays, we use computer-controlled milling machines that are breathtakingly capable. Back then you would just have a lot of machines and a lot of operators. One guy might perform the same milling process on a zillion pieces of stock sequentially passing them on to the next guy who did the next function. Do that enough times and you’ve built a bunch of guns.

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In the interwar years, gun designers began experimenting with different kinds of production techniques. The electrolytic extraction of elemental aluminum from bauxite ore introduced this material into the manufacturing milieu, particularly for aircraft applications. However, one of the most transformational additions to the industrial landscape was the perfection of mechanical stamping techniques.

Sheet Steel Stamping: The Keys to the Kingdom

Imagine you take a standard green Army man from your childhood and press him face first into a generous block of Silly Putty. Once you remove the Army man you have a detailed impression left in the Silly Putty medium. Industrial metal stamping similarly uses male and female dies to form complex shapes in sheet stock.

As it applies to firearms, a stamping die is carefully cut from steel that is made tough and hard enough to withstand many thousands of mechanical cycles under extreme pressure. These dies are typically made male and female. There are dozens of considerations to include when making such stuff. A skilled die maker will take into account such things as mechanical springback and burr management as well as ensuring that the deformation is not so extreme as to render the final parts brittle. There is an art to this process. A successful die maker combines a baseline mastery of metallurgy and materials science with the knowledge of how these materials will behave practically that is borne of experience. Creating the dies required for industrial stamping operations is both tedious and expensive. However, the end result is the capacity to create vast quantities of identical stamped parts quickly and at very reasonable cost.

Industrial stamping can incorporate a variety of specific processes into a single die stroke. These can include punching, bending, embossing, flanging, coining, and blanking, to name but a few. Maintaining the required clearances, tolerances, and respect for the mechanical capabilities of the underlying material comes from experience and training. The design process leading up to a large-scale industrial stamping endeavor is time-intensive and complex.

There are three major types of stamping processes. Progressive die stamping incorporates a series of stations, each of which performs a separate function. In this way a piece of blank stock, frequently maintained on a roll, can be progressively manipulated to form complex shapes. Fourslide or multi-slide stamping involves the use of four different slides or tools that work a part simultaneously. This process allows for intricate cuts and complicated shapes along with greater flexibility for subsequent design changes. This equates out to versatility at the expense of speed. Deep draw stamping involves forming material into a part using a punch that defines the ultimate shape. The term “Deep Draw” applies when the depth of a part exceeds its diameter. Many automotive and aviation components are made this way, as are cartridge cases.

In the manufacture of cartridge cases, a single brass slug called a cup is drawn through a variety of sequential steps to form a complex ammunition case. When necessary the case is annealed at certain points in the process to soften the metal sufficiently to allow further deformation. Annealing is a type of heat treatment wherein a piece of metal is heated sufficiently to relieve internal stresses brought upon by mechanical deformation. By annealing these components stepwise, a relatively bulky starting substrate can be deformed into something truly extraordinary. By way of example, the cup that eventually becomes a .50-caliber BMG round starts out as a little chunk of brass about the size of my thumb.

Making Dies

The primary tools used to create forming dies are CNC milling machines and EDM cutters. CNC stands for Computer Numerically-Controlled, and these machines are simply amazing. Multi-axis machines can craft complex three-dimensional parts out of such stuff as steel and aluminum in a manner akin to sculpting. Various cutter bits approach the work from various directions, removing material until the desired part is all that remains.

Prior to beginning the machining process, design engineers use software like Solidworks to digitally craft a component electronically. In this way, dimensions and manufacturing efficiencies can be optimized prior to actually cutting any metal. These advanced software suites can even combine parts in the digital realm to ensure that tolerances are adequate and nothing interferes with anything else while in motion.

EDM stands for Electrical Discharge Machining. This process is also known as spark machining, spark eroding, die sinking, wire burning, and wire erosion. In this case a series of rapidly recurring electrical discharges run through a thin brass wire is used to make incredibly precise cuts even in thick, heavy material. The process must be undertaken between two electrodes separated by a dielectric liquid.

This process was pioneered during World War 2 by a pair of Soviet scientists investigating a cost-effective method for cutting tungsten, and exceptionally hard element. At the same time but independent from their Soviet counterparts, a group of American scientists was perfecting the same process for use in removal of broken drills and taps from aluminum castings. Nowadays EDM machines are common in most well-equipped tool and die shops. A proper machine shop is a veritable playground for me. Amidst a myriad of cool mechanical toys to be found therein, the EDM machines are my hands-down favorite of them all.

Applications

That’s a lot of tedious technical stuff for a gun magazine, even one as highbrow as Firearms News. However, the ultimate impact these techniques have had on the modern gun world would be tough to overestimate. Evidence of such stuff surrounds you every time you visit the local gun emporium. The most stark delineation between the processes of machining and stamping can likely be found in the wartime German MP38 and MP40 submachine guns. These two weapons are externally very similar. You could be forgiven should you have difficulty telling the two guns apart in dim light. However, their manufacturing techniques were altogether different as driven by the exigencies of total war.

The MP38 was likely the first mass-produced military weapon to eschew wood of any sort. The receiver for this open-bolt, blowback-operated submachine gun was machined out of a piece of drawn steel tubing. This means that the Germans took a piece of steel pipe and then cut away everything that wasn’t an MP38 receiver using machine tools. The end result included longitudinal flutes machined in to minimize weight and maximize stiffness. The pistol grip/fire control unit of the MP38 was machined out of an aluminum casting as well.

The subsequent MP40 looked about the same, but its receiver began life as a sheet of steel stamped out and folded over a mandrel. The MP40 fire control unit was also stamped out of sheet steel as well. Additionally, the barrel was slipped in place and secured through an industrial stamping operation that mashed the receiver wall into grooves cut in the trunnion. The end result, once all the dies and such were perfected, allowed semiskilled workers to churn out vast numbers of components at very reasonable cost in a short period of time.

The MP43 assault rifle was the next step in this mechanical evolution. Everything that could be stamped on the MP43 was stamped. This included the receiver, the rear sight base, the ejection port cover, the fire control unit, the magazine, the front handguard, and the stock mount. These pieces were then welded together as needed. These streamlined techniques allowed the Germans to produce 425,977 copies in less than two years despite aggressive strategic bombing and an omnipresent shortage of raw materials.

Meanwhile on our side of the pond, the Guide Lamp division of General Motors was churning out M3 Grease Guns. These stubby utilitarian pressed steel submachine guns were designed from the outset to be cheap and easy to make. The Grease Gun receiver was stamped as two mating halves that were subsequently welded into a functional whole. The front aspect was threaded to accept the barrel nut. While the end result was undeniably ugly, the weapon was compact, reliable, and effective. I shoot markedly better with the old Greaser than I do with the much more expensive Thompson SMG.

Ruminations

Mechanical evolution marches on. Nowadays aluminum casting techniques combine with high speed mills to facilitate such stuff as low cost AR-15 receivers. Mass-production mills churn out components like pistols slides multiple copies per cycle. Such stuff is precise, strong, and lightweight. However, industrial stamping still shapes the gun landscape even today.

All of the roller-locked HK guns and their clones are built around low-cost stamped steel receivers. The same can be said for the CETME-L from Marcolmar. Additionally, if you have ever driven a car, used a clothes drier, or cooked on a stovetop you have likely benefitted from some sort of stamped steel components. Likewise, the chassis of every desktop computer on the planet began life as a flat piece of sheet steel punched, bent, and formed into shape. All of these commercial products are built using the same industrial stamping techniques perfected in the manufacture of war materiel during World War 2.

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About the Author

Will is a mechanical engineer who flew UH1H, OH58A/C, CH47D and AH1S aircraft as an Army Aviator. He is airborne and scuba qualified and summited Mount McKinley, Alaska, six times…at the controls of an Army helicopter. After eight years in the Regular Army, Major Dabbs attended medical school. He works in his urgent care clinic, shares a business building precision rifles and sound suppressors, and has written for the gun press since 1989.

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