Weapon lightweight is the research focus of weapon industry and an important means to improve individual combat capability. At present, engineering plastics have played an important role in the field of military industry, and have gradually become an indispensable material for the development of new weapons from a substitute in the weapons industry.

At the end of the 20th century, the rise of high and new material technology set off a new military revolution. High and new material technology refers to lightweight material technology, functional material technology, intelligent material technology, etc. They have a significant impact on modern warfare and have also changed the military weapon assembly. The technology of lightweight materials has made great contributions to the development of light weapons. While improving the lightweight, functional and high-performance of weapons, it also has a comprehensive and profound impact on the R&D and design of the next generation of new weapons.

Light weapons generally refer to the weapons carried by individual soldiers or teams in combat. They are of various types and can be assembled on various basic equipment. They can be used in a wide range. They are not only the main weapons of infantry operations, but also the general weapons and equipment of the whole army. Firearms and ammunition are the most commonly used light weapons.

The inexorable trend of the development of light weapons is the individual integrated combat system, which aims to maximize the individual combat capability, so that soldiers and weapons and equipment form an organic whole, thus comprehensively increasing the individual's survivability, lethality, mobility, command and control capabilities, and durability, and achieving a breakthrough in light weapons.

In the past, when evaluating the level of weapons and equipment, the performance of a single weapon was usually the main factor. Now, the evaluation criteria are whether a single weapon and a single combat unit as well as a joint operation system can achieve integration, connectivity and linkage. Integration is the inherent requirement of individual soldier system construction and the urgent need to integrate into the joint operation system.

Therefore, in order to achieve the "integration" of individual light weapons, while continuously developing new materials and improving the performance of light weapons, it is also necessary to find appropriate processing methods and efficiently customize weapons and equipment according to the individual needs of soldiers. The application of engineering plastics in light weapons can effectively realize the lightweight of weapons and promote the "integration" of individual light weapons. Since the middle of the 20th century, researchers at home and abroad have carried out a lot of exploration.

Main Applications of Engineering Plastics in Firearms

• Advantages and Requirements of Engineering Plastics in Firearms

The wooden parts on the firearms will become loose after being used for a period of time. The wood will be scorched during continuous shooting, easily broken during stabbing, easily mildewed in tropical areas, and expanded after rain to increase the quality. In addition, the wood utilization rate of wooden parts is very low, the processing technology is complex, and the quality is heavy. Using engineering plastic parts to replace wooden parts can effectively solve these problems. The advantages of engineering plastics are shown in Figure 1.

These characteristics make engineering plastics widely used in all aspects of firearms. On different components, there are different requirements for the performance of engineering plastics, as shown in Figure 2.

When used as stressed components and secondary stressed components, engineering plastic products should not only have wear resistance, corrosion resistance and aging resistance, but also have high strength, rigidity and toughness; When it is used as a high-frequency stressed component, the stress of the parts is more severe than that of the stressed components, and the force is large and frequent.

If the hammer in the combat state will fire hundreds or even thousands of bullets every minute, the hammer will be impacted hundreds or thousands of times, and the accuracy of the mechanism action is highly required, so there are more stringent requirements on the performance of materials. Such products must also have excellent strength, rigidity, toughness and impact fatigue strength; When it is used as a high-temperature and high-frequency load-bearing component in direct contact with gunpowder gas, its working conditions are extremely bad, and the temperature of the cartridge during firing is as high as 200~500 ℃.

Movable parts such as pistons and guns move back and forth thousands of times per minute, so high thermal deformation temperature is also required. Common engineering plastics cannot meet these requirements, so carbon fiber composites are often used to prepare such products.

• Application of Engineering Plastics in Firearms

Since the 1940s, engineering plastics have been gradually used in the manufacture of firearms. Steyr Manlichia Company of Austria is the first small arms manufacturer to use engineering plastics on firearms. The AUG5.56mm rifle developed by the company is a model for the application of engineering plastics in firearms, as shown in Figure 3 (a).

The rifle uses a large number of engineering plastic parts, accounting for about 20% of the total number of parts of the rifle. Its grip, butt, magazine, trigger, hammer and other parts all use engineering plastic parts.

In addition, the semiautomatic pistol SSP9mm and the material destruction rifle AMR15mm developed by Steyr Company are also widely used in engineering plastics and composite materials. The CLOCK 17 pistol developed in Austria consists of 34 parts, 14 of which are made of engineering plastics, accounting for up to 40%, as shown in Figure 3 (b). The sleeve seat is prepared by injection molding, and the parts such as magazine, base plate, sight, firing mechanism and clearance sleeve are also engineering plastics.

• Use of engineering plastics in firearms in the United States

In 1944, the 7.62mm Browning semi-automatic rifle developed in the United States usedglass fiber reinforced phenolic resinas the butt and guard, as shown in Figure 4 (a). Then usecotton cloth reinforced phenolic resinas the butt, guard, grip, magazine and other parts of AR-10 automatic rifle.

In 1957, the US military replaced the M147.62mm rifle. The rifle uses glass fiber reinforced polyester resin as the butt and guard wood, which improves the strength of the butt and reduces the quality by 30%. In the continuous firing of 500 bullets, the wooden butt is easy to burn and carbonize, while the plastic butt is basically undamaged, as shown in Fig. 4 (b).

Based on the research of M14 rifle, the butt, guard and grip of M165.56mm rifle are all made of fabric reinforced phenolic resin with high impact strength. The subsequent M16A1 rifle uses polyester polyurethane elastomer as the butt. The polyurethane elastomer contains carbon black, iron oxide and titanium dioxide fillers, which can increase its mechanical properties and UV radiation resistance. It can be molded once through plastic molding, and its overall performance is significantly better than that of phenolic resin butt, as shown in Figure 4 (c). In addition, the butt and guard wood of M16A2 rifle are made of super tough nylon, and the mechanical strength of the butt is much higher than that of M16A1 rifle.

As shown in Figure 4 (d), the AR-7 sports gun uses ABS resin to prepare the butt, front support and tool container, and the M60 light machine gun also uses this plastic as the grip; The butt of 5.56mm Remington rifle is made of nylon 66 by one-time injection molding. Most parts of the "nylon" rifle of the arsenal except the barrel are made of fiber reinforced nylon composites; The ASP9mm pistol uses polycarbonate as the transparent grip, and the 5.56mm and 4.32mm rifles use polycarbonate as the transparent magazine; The butt of the M86LR300 Winchester High Power Sniper Rifle and the M87ELR12.7mm Sniper Rifle are made of fiberglass.

• Use of engineering plastics in firearms in Russia and some European countries

The application research of engineering plastics in firearms in Russia started late. The cartridge case of AK-74 assault rifle developed in the 1970s was made of glass fiber reinforced thermosetting resin, which has good mechanical properties and is 28.5% lighter than the metal cartridge case, as shown in Figure 5 (a).

RPK-74 light machine gun uses glass fiber reinforced plastic to prepare the butt, as shown in Figure 5 (b). The magazine of AR-744.5mm assault gun is made of glass fiber reinforced polyvinyl alcohol modified phenolic resin.

Other typical guns containing engineering plastics in other countries include: the 22LR submachine gun developed in Yugoslavia uses a large number of engineering plastics composite materials, which accounts for far more than other submachine guns; the case is made by one-time molding; 176 transparent drums and a large number of small parts are made of fiber reinforced plastics; The P90 submachine gun developed by Belgium FN Company also fully uses engineering plastics. 27 of the 69 parts contained in the whole gun are engineering plastics, as shown in Figure 5 (c).

The butt of the Swiss STG905.56mm rifle is made of engineering plastic filled with synthetic foam plastic, and the cartridge case is translucent plastic; 33 parts of French FAMA S5.56mm rifle, such as butt and launcher base, are made of 30% and 60% glass fiber reinforced nylon 11, accounting for 16% of the total number of rifles, as shown in Figure 5 (d); The butt and grip of British PM sniper rifle and SAR-87 assault rifle are made of glass fiber and asbestos reinforced phenolic resin respectively; The casing of the shell free advanced combat rifle of HK Company in Germany is made of glass fiber reinforced nylon plastic, and the barrel and sights are made of high-strength engineering plastics through one-time molding.

• Use of engineering plastics in firearms in China

In order to reduce the quality of weapons and save wood, China began to study the application of engineering plastics in light weapons from the 1960s, and gradually went through the road of replacing wood with plastics, and replacing metal stressed components, sub stressed components, high-frequency stressed components and other key components.

The butt of the 56 type submachine gun [Figure 6 (a)], 56 type semi-automatic rifle and 63 type automatic rifle developed in China are all made of glass fiber reinforced plastics, and the wood guard, grip and magazine, oil pot and grip of the 63 type automatic rifle are all made of high-strength engineering plastics; In order to replace the 54 type 7.62mm pistol, China has independently developed the 92 type pistol, which uses the engineering plastic integral grip structure with good thermoplasticity and high strength to replace the traditional metal gun bottom handle. The processing technology is simple, the injection molding is one-time, and the consistency and economy are good [Figure 6 (b)]. 11 parts of 5.8mm first and second generation automatic rifles, such as butt, guard, grip and magazine, are made of glass fiber reinforced modified nylon 66 and nylon 610.

Since the industrialization of nylon 66 in the 1930s, engineering plastics have developed rapidly, with increasing types, and have also been widely used in firearms, as shown in Figure 7.

In 1961, DuPont successfully developed polyimide with excellent performance, opening a window for the development of special engineering plastics. However, special engineering plastics are not widely used in firearms. High performance engineering plastics with good heat resistance, abrasion resistance and corrosion resistance, such as polyetheretherketone, polyetherimide and polyphenylimidazole, are not widely used in firearms. In the future, in the process of improving service firearms and developing new firearms, such high-performance engineering plastics parts can be appropriately added to improve the performance of firearms in extreme environments.

• Existing problems and future development trend

Although engineering plastics have many advantages in the use of firearms, it also exposes some defects. For example, the 95 type rifle, which is the first large-scale use of engineering plastics in China, will appear white after friction, mildew after being affected with moisture and other conditions in the use process. This is because the engineering plastics are added with reinforcing fibers to improve its mechanical properties. Due to long-term friction, the fiber dimension is exposed, commonly known as the phenomenon of galling and whitening.

In addition, the five commonly used engineering plastics also have the following problems.

(1) High shrinkage, poor dimensional stability, high water absorption, larger size in wet environment, affecting the precision of parts.

(2) It has low hydrolysis resistance, is sensitive to notch, has poor chemical resistance, abrasion resistance and scratch resistance, and will turn yellow when exposed to ultraviolet light for a long time.

(3) It is not resistant to acid, strong alkali and solar ultraviolet radiation, and has poor weather resistance and high temperature thermal stability.

(4) Poor light resistance, poor melting fluidity, poor resistance to inorganic acids, alkalis, aromatic hydrocarbons, halogenated hydrocarbons, oils, etc.

(5) It is easy to decompose in case of water, and should not be used in high temperature and high humidity environment.

In order to solve the above problems and enable the plastic components on the guns to be used in harsh chemical and physical environments for a long time, it is the most common method to modify engineering plastics and prepare engineering plastics composites. At the same time, developing new engineering plastics with higher comprehensive performance and improving the processing methods of engineering plastics parts are also important means to improve the performance of engineering plastics parts.

Reference: Application and Development of Engineering Plastics in Light Weapons [J] Wang Pei, Xia Liu, Cai Huanxi, et al. Science, Technology and Engineering, 2022, 22 (13): 5095-5105