M4/M4A1 carbine

                                              M4/M4A1 carbine

                                    Caliber:　5.56 × 45mm M855

With the successful development of the M16A2 , the US military has also begun to consider developing a new carbine firing SS109/M885 bullets for special forces. Like the M16A2 , this new carbine was designed in 1983 based on the needs of the Marine Corps . At that time, the Marine Corps' Expeditionary Force was directly affiliated with the Reconnaissance Company (i.e. Force Recon , which in the past was always literally translated as "force" or "force". In fact, this refers to the "Marine Expeditionary Force (Marine Expeditionary Force)") . The only small shoulder-fired weapon officially issued was the M3A1 "greaser gun" (unofficially the XM177E2 ), and the armored crews also used M3A1s , and the Marine company thought that these people should be provided with a carbine. Initially, the M16A2 carbine developed by Colt for the Marine Corps basically just applied the changes on the M16A2 to the Model 653 carbine, that is, the 14.5-inch (368mm) heavy barrel with a 1/7 twist rate was replaced with the M16A2 eliminater . Flame weapon, using 3- round burst fire instead of full-automatic shooting, and using the M16A2 mechanical sight. This M16A2 carbine was designed in 1985. It was designated the Colt Model 720 and was called the XM4 in the military's test program . However, Congress rejected the Marine Corps' XM4 procurement budget. As a result, the expeditionary force's direct reconnaissance company had to use the Navy's HK MP5-N submachine gun to replace the old M3A1 submachine gun, while other US military special forces began to use the RO727 in 1988. Wait for other M16A2 carbines .

The U.S. Army's Test and Evaluation Command (TECOM) resumed development and Phase 2 testing of the XM4 carbine in April 1986 . After further testing and improvements, the XM4 was officially finalized and named "The United States Carbine, Caliber 5.56mm NATO, M4" in March 1991 . The most obvious distinguishing feature of the M4 from other M16A2 carbines is that its barrel has a constricted shape 25mm in front of the quasi-constellation. This was a change made in later tests to accommodate the M203 grenade launcher. In order to be able to mount the original M203 grenade launcher, the barrel diameter of the M16A2 inside the handguard is the same as that of the M16A1, but the carbine's handguard is shorter and the M16A2-style thick barrel is used outside the handguard, so the Colt Engineers from China processed this constriction in the middle of the barrel outside the handguard so that the M203 grenade launcher can be mounted. A fixed stock can also be attached and used, but this is not common in the US military.

The M4 Carbine also changed the telescopic stock that originally had only two fixed positions to four fixed positions, and later to six. In addition, although the rear sight of the M4 is M16A2 style, the rear sight can only be adjusted to a maximum distance of 600 meters instead of the 800 meters of the M16A2 . Since the lower receiver is M16A2 , the shooting mode is semi-automatic and three-round burst. Since the M4 and M16A2 are so similar, in fact 80% of their parts are interchangeable, it was also originally called the M16A2 Carbine . The M4 was first equipped with the 82nd Airborne Division and was used to replace the M16A1/A2 rifles, M3A1 submachine guns and some 9mm pistols used by vehicle drivers . It was officially installed in 1994 .

The M4 carbine first participated in actual combat in the Gulf War in 1991. Before the war broke out, the U.S. military suddenly discovered that they were short of new rifles. Many troops were still using the M16A1 , while the M16A2 only began to be equipped in 1986 , and many troops had not yet completed the replacement. . Due to the need to obtain large quantities of M16A2 and M4 as soon as possible , the U.S. Department of Defense approved the increase of M4 suppliers. Bushmaster Firearms of Maine obtained a procurement contract to supply M4 carbines and supplied 4,000 to the Army . An M4 , these guns were used by the 82nd Airborne Division during "Desert Shield" and "Desert Storm" . It is said that General Schwarzkopf's escort also used Bushmaster M4 . However, the U.S. military had not yet obtained the production rights for the M4 at that time (because the U.S. government had already obtained the production rights for the M16, so the M16A2 production contract could be awarded to FNMI that year). Colt threatened to sue the U.S. government for selling to other companies without permission. After transferring the M4 's process documents, Bushmaster only got this one government procurement contract for the M4 .

Schwarzkopf's bodyguard during "Desert Storm" in 1991 was thought to be an M4 due to the shape of the carbine, but it is said that his personal bodyguard was actually a Delta member, so it should be a Type 723

M4 receiver with fixed carrying handle

On the M4 in early trials , the rear sight on the handle was M16A1 style and was not adjustable for windage.

An early experimental M4 using a 90-round WMG drum magazine

Different barrel types tested in XM4 trials

XM4 prototype gun tested by the Marine Corps in 1989, with different barrel shapes

One of the heavy barrels in the XM4 test Colt M4 MWS with a flat-top receiver , when the handle is not used, the M4 MWS can use folding iron sights                                        Detachable carrying handle for M4A1 and M4 MWS The white aluminum double-layer heat shield inside the handguard can reflect the heat of the barrel. When the barrel overheats, the handguard will not be too hot to hold. The M16A2 (top) has only one layer of heat shield The barrel of the M4 /M4A1 has a three-section shape . A small constriction cut out of the front end of the barrel is used to fix the front part of the M203 mounting rail . The method of attaching the M203PI grenade launcher to the M4 /M4A1 is the same as the M16A2, but there is no special handguard. This short-barreled Remington 870 shotgun hung under the M4 barrel is designed to enhance close combat capabilities . It is only an experimental model and has no official name. Generally called Masterkey, this name also indicates that one of its uses is to break doors. Seal from the early 1990s, using a carbine that may have been the RO727

A picture of the M4 from the 2002 U.S. Army Weapons Manual. The M4 in this picture still has a fixed handle.

This is the flat-top receiver M4 and M16A2 of the Marine Corps. From this picture, you can see that the M4 flash suppressor is the same as the M16A2 flash hider, with the two lower openings eliminated.

Flat-top receiver M4 in the Army M4 MWS, flat-top receiver and RAS handguard equipped by the US Marine Corps in Iraq in 2002 M4 modified and painted by soldiers themselves The blue barrel is a kit that replaces the Fx reactive bomb These are all methods of replacing the M4A1 with a fixed stock , not purchasing the civilian KAC SR15. The M4A1 of the reconnaissance company directly under the Marine Corps Expeditionary Force in the Iraq War in 2003 looks no different from the M4 MWS in appearance. Close-up of the Army M4 MWS. The mark on the speed controller is "burst fire" rather than fully automatic. This is a weapon for conventional forces rather than a weapon for special forces. Thanks to William James for providing the photo. It seems that all US Army equipment in 2010 was marked with a QR code. Looking at the surface treatment of this receiver, no wonder a retired former Marine told me that holding a Colt M4 with Comparing FNMI's M16A4, I always suspect that Colt's M4 is OEMed in China. M4 MWS as a self-defense weapon for the Aberdeen crew

After the M4 was equipped with troops, Colt designed a flat-top receiver that used Picatinny rails instead of fixed handles to facilitate the installation of modular aiming devices. In August 1994, this improvement was also accepted by the US military, and this flat-top M4 was officially named "The United States Carbine, Caliber 5.56mm NATO, M4A1". The Colt number is 927. Since special forces did not like the burst-fire limiting device of the M4 carbine and used other M16A2 carbines that could fire fully automatically, the M4A1 also used the lower receiver of the M16A1 . However, during the test, it was found that the barrel of the M4A1 is prone to overheating. After a shooter fired six magazines in a row in fully automatic mode, the handguard became too hot to touch directly. Although the M4A1 is a carbine rather than a light machine gun, Colt improved the handguard to solve this problem and changed the aluminum heat shield from the original single layer to a double layer, so the guard was thickened accordingly. Wood diameter. This improvement was later applied to the newly produced M4 carbine, so the handguards on the early M4/M4A1 were the same as those on the previous M16 carbine, while the later M4/M4A1 handguards were thicker.

In 1994 , the Marine Corps published "Operational Requirements Document 1.14. " (Operational Requirements Document 1.14.), which stated that it took a long-term view of the mission of the expeditionary force's direct reconnaissance company and used the M4A1 carbine to replace the MP5- fired pistol ammunition. The N submachine gun will be more effective as a CQB weapon. After some efforts, the Marine Corps finally obtained funds to purchase the M4A1 , but mainly to equip special forces. The U.S. Army also officially adopted the M4/M4A1 carbine on August 15, 1994 , first equipping special forces and rapid reaction forces.

Most of the M4 carbines with a limit of 3 rounds are equipped with crew members, crew members, clerks or officers. For example, M1 tank crew members have used four M3A1 submachine guns as self-defense weapons for many years, but now they use two M4 carbines and two M9 pistol. Since the flat-top receiver is convenient for installing sights, except for the early orders with A2 handles, all M4s purchased by the US military now use flat-top receivers. The sights are mainly Trijicon's TA11 and TA31 ACOG and Aimpoint M68 CCO. The current government standard M4 series are Colt Model 920 (flat-top M4, speed machine "S-1-3") and Colt Model 92 1 ( M4A1, speed machine "S-1-F") .

The Colt Model 925 carbine equipped with the KAC M4 RAS handguard was tested and designated the M4E2, but this designation appears to have been abandoned due to confusion over whether existing carbines needed to be renamed when the handguard was installed. The U.S. Army Field Manual refers to the M4 series equipped with RAS as the Modular Weapon System (Modular Weapon System) or M4 MWS for short.

The following table is from the April 2003 version of the FM23-9 manual. The M4 in this table is the M4 MWS that has been replaced by RAS, so its weight is heavier than the plastic handguard M4 in the table above, and even heavier than the M16A1 . Heavy. In addition, the muzzle velocity in this table is different from the table above, which may be due to differences in the testing environment, such as the influence of temperature and pressure.

Although the M4A1 was developed for Special Forces, the Army announced in 1998 that it planned to replace the M16A2 with the M4A1 with a RAS handguard as the standard rifle in regular forces , while the original M16A2 was transferred to the Reserve Forces and Coast Guard (Note: Also Some information indicates that the replacement plan started in November 1997, and it is planned to be completed by the end of 1999). Why would the Army want to replace the standard assault rifle with a carbine? The Army's explanation is that the M4A1 is lighter than the M16A2 and is effective enough to deal with targets within a 200- meter range; another explanation is that when the "Land Warrior" system is equipped with troops, the M4A1 can reduce the total weight of the system. But there is actually another rumor that some senior generals within the Army are still very upset about FNMI beating Colt to obtain the M16A2 supply contract in 1988 due to its price advantage , because FNMI is a foreign-backed company. If the Army decided to adopt a different model of rifle, it would have reason not to continue with the purchase contract with FNMI. However, in fact, the Army ultimately purchased large quantities of the M4 MWS from Colt, which could only fire three rounds, instead of the M4A1.

There was much controversy surrounding the purchase of the M4 MWS, and when Colt was awarded the Army production contract, FNMI immediately proposed that they could also produce the M4 for the Army . The Army rejected the offer, and FNMI filed suit in U.S. federal court, arguing that it was unfair for the U.S. government to appoint the sole contractor. A federal court dismissed FNMI's complaint following Colt's campaign, explaining that the M4 series' technology was proprietary to Colt and was granted a 10-year license under a December 1997 agreement between Colt and the Army . exclusive purchasing rights, and stipulates that the military shall not grant production rights or transfer process documents of the M4 series to other manufacturers before 2011 .

The peak of the Army's procurement of M4 MWS was around 2000. In 2001 , the US Army finally decided to equip regular troops with the M16A4 with RAS handguards . This seemed to be evidence of that rumor. The Army still purchased M16A4 from Colt. The Marine Corps purchases the M16A4 from FNMI. Someone who retired from the U.S. Marine Corps said: The quality of FNMI's M16A4 is much better than the Colt M4. When compared together, it almost makes people suspect that Colt is OEMed by a Chinese factory.

Since the shorter barrel results in lower muzzle velocity and greater muzzle noise, and the handguard is more likely to heat up than a long rifle, the Marine Corps has repeatedly debated whether to adopt the M4A1 or retain the M16A2 , and finally in September 2002 It was announced in March that the M16A2 will be replaced by the M16A4 with a RAS handguard , but it will be produced by FN. Many dismounted infantrymen on the battlefield in Afghanistan complained about the shortcomings of the M4 series' insufficient range, which promoted the decision of the Marine Corps. However, in the urban combat of the invasion of Iraq in 2003 , those mechanized infantrymen who still used the M16A2 believed that They need short and powerful light weapons like the M4 even more. This is because the fighting distance in the city is much closer than in the mountains of Afghanistan, and even when fighting in the suburbs, these members of the mechanized force do not need to use the light weapons in their hands to deal with targets 300 meters away. , and those troops who complain about the insufficient range of the M4 are mostly light infantry who lack heavy weapons support.

Although the effective range of the M4 series is not as far as the long-barrel M16 series, many military analysts believe that infantry light weapons do not need to shoot at 300-meter targets in most cases, as long as they are effective within 150m, it is enough. The M4 series is favored by counter-terrorism forces and special forces due to its compact shape and powerful firepower (only the fully automatic M4A1) is suitable for CQB. These advantages are also suitable for urban combat, so in infantry squads of conventional forces, the M16A4 is the Mainly paired with a small amount of M4 MWS has become a popular model. Among quick reaction forces such as special forces and airborne troops, the M4A1 is the main battle weapon. The United States Special Operations Command (USSOCOM) adopts the M4A1 as the standard rifle.

Comparison between a heavy barrel (top) and an ordinary barrel commonly known as a "pencil barrel" (bottom). The difference lies in the part wrapped in the handguard. The guns ordered by SOCOM have always had heavy barrels.

In recent years, Colt has produced M4A1 or modification kits with a thickened inner barrel of the handguard. Although the overall thickness of the barrel will slightly increase the weight, it is more heat-resistant and more accurate when firing fully automatically. These heavy-barreled weapons also come with a new, slightly heavier buffer called the H2. The standard H shock absorber has a sliding weight consisting of one tungsten and two steel pieces, while the new H2 shock absorber has two tungsten and one steel pieces. These weapons are currently known as the Colt 921HB (heavy barrel), but the HB improvements adopted by the military were not renamed, so the government M4A1 includes the 921 and 921HB. In fact, the M4A1 ordered by USSOCOM has always used a heavy barrel, which has always been different from the M4A1 ordered by other units.

In addition to being equipped in the US military, the M4 series is also exported to other countries, and Colt also provides four models of M4 /M4 A1, RO 777, 779, 977 and 979, to law enforcement agencies .

Since Colt's exclusive purchase rights for M4 carbines expired in 2009, the U.S. Department of Defense has been delaying finding a second supplier. It was not until April 2012 that Remington was finally identified as the second supplier and a production contract for 24,000 M4s was signed, with delivery starting in 2013. On average, each gun in this contract, together with accessories, spare parts and after-sales service, costs about US$3,000, and the price quoted for each gun is US$673. When Colt held the exclusive purchasing rights, the price quoted for a single gun actually exceeded US$1,000.

In 2012, Remington defeated Colt in bidding and won a $77 million M4 production contract from the U.S. Army. However, Colt protested to the U.S. General Accounting Office, believing that the calculation of the M4's patent fees was improper. Incorrect, allowing Remington to win the contract at a lower price. So the General Accounting Office had to re-tender, and the second tender was won by FN Company in 2013. As a result, FN Company not only became the supplier of M16A2 and M16A4 to the US Army and Marine Corps, but now also became the supplier of M4 to the US Army. business.

In May 2014, new changes occurred. The U.S. Army began to gradually upgrade all M4s on hand into M4A1 . In addition to replacing the fully automatic trigger group, the transformation project also replaced the heavy barrel (the thin diameter barrel behind the gas hoop was also changed to a thick diameter), and replaced it with new Double-sided operation safety/speed machine handle. The modification process is not to use the stock M16A1 lower receiver like the Navy's Mk.18 , but to send the existing M4 to the Army's logistics repair shop to replace spare parts and re-engraving. For example, the original "BURST" mark on the "burst" position of the speed machine is erased by marking four "X"s with a laser, and then adding "AUTO" underneath. These modifications are not carried out in the same factory, but may be sent to each base's own repair shop for completion.

The repair shop located at Fort Riley is one of the units involved in modifying the M4. This unit provides logistics and maintenance services to the First Red Division.

The worker disassembled the lower receiver, removed the trigger group, put it into the machine to re-engraving, and then installed the fully automatic trigger group.

Modified M4A1

In fact, some troops began to try to replace the M4 on hand with M4A1 around 2012 , but it was not until 2014 that the Army made the decision to replace all of them. This renovation lasted until 2015. But this is only the first phase of work. It is said that there will be a second phase, which will upgrade the rail system, bolt and bolt group, and also plans to replace the trigger group with a light trigger of about 4 to 5 pounds (many people speculate that SOCOM The Geissele trigger developed by the company is likely to win the bid); there is also a third stage, which may improve the gas system (but there is no proposal to replace it with a piston system). (Thanks to nedbrucet for the information)

From then on, the M4 no longer existed in the U.S. Army, only the M4A1 remained .

The lower receiver produced by FN was originally M4 and was modified into M4A1