Structure, Glue and Engine
By Paul Evancoe
There are three essential elements in all firearms that determine the reliability and operational life expectancy. They are: 1) the metallurgical composition of the firearm’s critical working components, 2) the screws that hold the component parts of a firearm together and 3) the springs that store and discharge energy in order for the firearm to operate properly.
First, a brief explanation of some of the metallurgy involved. Metal alloys are assigned a formulation reference number that delineates the unique qualities of that particular metal. These unique formulation recipes are assigned numbers by ASM International, formerly known as the American Society for Metals.
ASM is a professional organization for materials scientists and engineers. ASM provides several information resources, including the ASM Handbooks; a series of reference books that provide data on various types of metals. These handbooks are recognized as a standard reference in the field of materials science.
Steels that contain carbon as the primary alloying element are referred to as carbon steels; generalized as high, medium and low carbon steel. They also contain small percentages of silicon and manganese. Additional elements such as molybdenum, chromium, nickel, copper, and aluminum are formulated into the alloy to achieve the exact metal characteristics desired for a particular purpose. So, as a basis for alloy formula that determines the metal’s hardness, wear resistance, ductility, machinability performance, the alloy is assigned a numerical figure recognized as an ASM number.
For example, ASM 1144 “Stressproof” metal and ASM 1144 “Fatigueproof” metal used in quality gun screws, are trademark versions of the 1144 formula. The patented formula and trademark name simply guarantees the 1144’s minimum qualities by the manufacturer. Whereas 1144 CD (cold drawn) metal, for example, while entirely acceptable for use in precision screws, does not have guaranteed characteristics and requires a more involved machining process. This translates to more material waste and more machining time required to reach the finished product.
1144 Fatigueproof steel is the choice of alloys for precision screws, but very few high quality screw manufacturers use it because it costs a bit more than generic 1144.
But few understand that there are screws and then there are “action” screws. For the purpose of this discussion we will define action screws as those screws that hold a firearms’ critical operating parts together. Screws used in receivers, bolts, bolt carrier groups, side plates, etc., that are subject to expansion and contraction from heat and the applied (sheering and torque) stresses, resulting from the weapon’s operations. Action screws are tightened to a design torque tolerance and cannot fail or the firearm will malfunction, or best case, the firearm will still operate but be unsafe.
Some of the higher end guns are manufactured using precision-made action screws that are specifically made for the purpose of joining critical parts. Lower end gun manufacturers buy their screws off-the-shelf and trim them to the desired length. Why is this a critical issue? It’s because not all screws are created equal. What does that mean? It means that most off-the-shelf screws are not manufactured in a precision machining process. They are die-forged to rough shape and dimension from wire stock. They are then roll-threaded by passing the unthreaded smooth round shank between threading rollers.
These rollers press threads into the screw’s shaft and a threaded screw falls out the back end of the threading machine. This results in a threaded screw that fits the hole, but it’s far from a precision-machined thread cut screw that will survive the rigors of thousands of rounds and will last a lifetime. Mass produced screws that have been trimmed to length or modified in some way to fit a firearms purpose are the type found in hardware stores and offered in discount parts catalogs.
By using these mass-produced screws in the gun assembly, the firearms manufacturer keeps his parts costs down and his profit margin up. Sadly, these screws lack precision head-to-shank concentricity (axial alignment of the screw head and screw shaft).
Secondly, their threads are not machine cut precision threads and thus they more easily strip when torqued or will slip resulting in torque forfeit. Third, because they are most often fabricated from less than optimal steel alloy they will sooner or later fail (break or sheer) from metal fatigue, and backing a broken screw out of a firearm is always ugly.
How are 1144 fatigueproof action screws made? They are custom designed precision action Hex head (as opposed to blade head) screws that are mostly made on Brown and Sharpe, or Swiss precision screw machines. They may appear to be similar to cheaper mass produced factory blade head screws but they are far superior. Many have Hex heads that require an Allen wrench to tighten. Allen head screws are used for applications that require consistent action screw torque settings, because the screw heads strip less easily than blade head screws so attaining the exact torque is easy.
Here’s how to tell what kind of screws are in your gun. Obviously, you can’t tell what alloy the screw is made from, but you can tell the difference between a good screw and a cheap one by examining its head and concentricity. Quality screws generally have Hex heads and are concentric to the shaft of the screw so they torque straight and true. Roll the screw on a perfectly flat counter top and see if its head and shaft are concentric. Also, quality action screws are only threaded where they need to be and not all the way up to the head of the screw. Full-length threading is a good indication that an inexpensive screw has been modified for action use by trimming its length. Quality action screws are most often entirely finished with black oxide or they’re blued. Be leery of screws that have finished heads but shafts left in the white.
If your gun(s) don’t have quality action screws, you may want to replace them with the quality variety. Quality action screws are made in the United States of America, not imported from China or elsewhere. Precision action screws are available online from several U.S. precision screw manufacturers who offer custom-made replacement action screws for your gun. Buy American.
If screws are a gun’s “glue” then gun springs are the “engine.” Gun springs are some of the most important parts in any firearm and shooters almost universally overlook them. Like screws, not all springs are created equal. Plain and simple - if you’re still using the original factory gun springs that came in your firearm, it is most likely not performing at optimum.
Most gun manufacturers do not make their own gun springs in-house. Rather, they buy them from various vendors (at best value) who make their springs from coiled music wire to the firearms manufacturer’s specification within a plus-minus tolerance. Quality assurance attention, while observed to one degree or another, is not observed on each and every spring. The result is a spring that meets a particular factory specification tolerance window, but is far from optimal in material or construction.
Does it get the job done? Yes, for a while, but ironically, a conventional music wire gun spring begins degrading the moment it is installed, and it degrades further with each compression. On average, a firing pin striker spring, for example, will exhibit up to a 30% loss of power eighteen months after installation without even being used. That’s a significant degradation by anyone’s math.
There is simply no way a gun spring in this degraded condition is capable of producing the energy required for consistent and reliable primer ignition. While it may drive the firing pin far enough forward to strike the primer and dent it, it may lack sufficient energy to strike the primer hard enough to ignite it. The result is a head scratching random misfire every several rounds that is most often blamed on a dirty gun, bad ammunition or a bad attitude (which generally manifests itself from misfires and can be heard above the decibels of gunfire; expressed in four letter words embedded in short declarative pronouncements). If only we realized our problem was as simple as replacing a bad firing pin spring.
The alloys used in gun springs significantly differ from the alloys used in screws. Gun spring alloys are formulated for ductility, flexibility, and to vigorously return to their non-compressed form (shape) when their dynamic constraint is released. In other words, they reliably return (spring back) to their full non-compressed form when they’re released or vice versa.
Modern metallurgy offers us quality gun springs that are made from chrome silicon or high-grade alloy spring wire that has been cold drawn and heat treated for consistent dimension and internal metallic granular structure. These modern alloys have added listing with the American Society for Testing and Materials (ASTM). For example, music wire springs may be phosphate coated, galvanized, tinned or cadmium plated, depending upon their purpose, and all bear the same ASTM-A-228 number. Stainless steel spring wire may be type 302/304 or type 316 nickel coated or soap coated, and bear the same ASTM A-313 number.
Many of today’s magazine springs are more of a metallurgical art form than they are a simple elevating force for the cartridge stack. They are in many cases, the most expensive part of the magazine for that very reason. Magazine springs are purposefully designed to provide robust and consistent tension (energy) against the bottom of the cartridge stack, so it is held in precisely the right position for proper feed. As in most all firearms’ springs, the secret is to formulate alloys for magazine springs that do not obtain a “memory” after months or years of full compression (being loaded). Many older magazine springs prior to the mid-1980s, are not made from modern alloys and have memory issues if they’re kept loaded.
To accomplish the task of eliminating magazine spring memory, design engineers many times not only optimize the alloy used in a quality magazine spring, they design a spring twisted from several wires. This “gangs” the spring qualities of several smaller wires into a larger wire strand multiplying the attributes of several into a superior single “gang” that is stronger, lighter and longer lived than using a single wire spring formed from the same alloy. It’s an art form on a macro scale.
Most modern factory magazines and some high-end after-market magazines can remain fully loaded for years without fear of spring memory. This is not the case for older magazines or cheap after-market magazines. If you’ve been keeping your magazines loaded for months or even years at a time, it’s best to replace your magazine springs in older factory magazines. If you have any after-market cheaply made magazines, replace them with new high-end or factory magazines.
Whether you are a competitive shooter or a casual plinker, a hunter of varmints, birds or big game, or carry in self-defense, you owe it to yourself to have the best screws and gun springs available installed in your firearm. The metallurgy provides the structure; the screws are the glue that holds it all together, and the springs are the engines of all firearms. If your life depends on that firearm, you need to make sure it works reliably when you need it most.
This article first appeared in Small Arms Review V21N5 (June 2017) |
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