In the early 1950s, Britain developed a 0.280-inch (7mm) bullet. If it had been adopted by the United States at that time, the history of bullet development would have been rewritten. At that time, the candidate gun provided by Britain to NATO was EM2 rifle. The gun adopts unsupported structure, with a caliber of 7mm and a muzzle velocity of about 771m/s.
In addition, the original FNFAL rifle also used this bullet. However, the US Army insisted on using 7.62×5 1mm "full power" bullets at that time. After persuading NATO to adopt its "full power" bomb, the United States advocated NATO to adopt 5.56×45mm bullets a few years later. If the 7.62 mm bullet is too powerful, then the 5.56 mm bullet is obviously insufficient in military power.
The barrel length of M 16 rifle is 508mm. Initially, M 193 bullet was fired, with a warhead mass of 3.56g and a muzzle velocity of 1000m/s ... American special operations forces adopted M4/M4A 1 series carbine as the standard. The initial velocity of SS 109 is 906m/s, which is lower than that of M 16A2 rifle. When launching SS 109 with M 16A2, the flying distance of the warhead with large trauma effect is about 200m, and then the warhead speed drops below 731m/s. ..
When SS 109 is fired with M4 or M4A 1 carbine, this velocity value appears less than109 meters ... This is the reason why the SS 109 bomb has insufficient lethality in Afghanistan and Iraq. Many action summary reports indicate that the trauma effect caused by M4 is only equivalent to 0.22 inch (equivalent to 5.59 mm) Ma Genan bullet.
In view of the insufficient lethality of M4, US special operations forces ordered new 5.56mm bullets with improved terminal ballistic performance, namely Mk262Mod0 and Mod 1 bullets. Some troops no longer believe that any kind of 5.56 mm bullet can meet the needs of special operations, so they began to explore alternatives.
There are several requirements for developing a new type of bullet. Most importantly, the new bullets can be used as active weapons, so that the army does not need to buy new weapons, and the new bullets can be fired by replacing the M4 carbine with new shells. The specific performance requirements of this kind of bullet are that the range, kinetic energy, lethality and killing range are better than those of SS 109 bullet, in addition, it is necessary to reduce the wear on the barrel and improve the service life of the weapon.
The M468 development project actually started in early 2002, when there was a report from the battlefield in Afghanistan about the insufficient lethality of SS 109 bomb. The bullets for this project were designed by Remington, and the partners included the US Army Special Forces and the US Army Shooter Training Camp in Fort Benning, Georgia. The designer of the new carbine box is Barrett Weapons Manufacturing Company of the United States. The magazine capacity is 5 10/0,28,3030 rds.
Starting with the German 7.92 mm bullet in World War II, the researchers investigated the whole development process of the intermediate bullet. 7.62× 39mm bullets are excluded from the candidate range, mainly because there is no ready-made magazine that can be reliably supplied from the standard M4 carbine. In other words, if this kind of bullet is to be used, a brand-new magazine must be designed.
Subsequently, the 6 mm, 6.5 mm, 6.8 mm, 7 mm and 7.62 mm bullets were investigated and tested, and the final conclusion was that the 6.8×43 mm special bullets had the best comprehensive performance in terms of accuracy, lethality and reliability.
Any department using M 16 rifle or M4 carbine can make the original gun fire 6.8×43mm bullets by changing the upper shell developed by Barrett Company. The changes to the upper shell are limited to the barrel and barrel base, gun puller and bolt machine, and of course, 6.8mm magazine is needed.
There are some other changes in the external configuration of this rifle. All M468 will be equipped with American Weapons Company's guideway system to add sight and accessories. This guide rail system makes the barrel completely float, that is, the barrel is not fixed at the front and rear points, but only installed at the front end of the casing to form a floating state, which enhances the versatility compared with the traditional wood protection system.
Because the diameter of 6.8mm is obviously larger than the original 5.56mm, and the outer diameter of the barrel is increased, the air guide hoop must be adjusted. Barrett does not slot the barrel, but sets an air guide hoop with a lifting lug, which is also used as a quasi-constellation and muffler interface.
The air guide ring is installed by the rotating shaft instead of the tapered pin in M 16. This can not only ensure that the air guide hoop is in place correctly, but also avoid the adverse influence of the open groove on the wall thickness of the cylinder. M468 spare mechanical sight can be folded backwards, and it will not block the line of sight when using optical sight.
Designed by Barrett Company, the sight can be folded horizontally and locked vertically, and can also be adjusted with equipped tools. The photo door is specially designed by American weapons company for its guide rail system. This is a door with two holes, one is shot from a distance and the other is shot from a close distance.
Muffler interface is unique, which is based on Barrett muffler patent design. The interface is a part of the air guide ring. When installing the muffler, remove the knurled retaining ring, tighten the muffler, lock the muffler in place through the clamping pin, and then press the clamping pin to release the muffler.
The frame of the bolt is a standard assault rifle, but the bolt has been greatly modified to adapt to the larger bottom of the 6.8 mm special bullet. The lock bamboo shoots have also changed, and the shell-taking hook has been slightly expanded, equipped with two more powerful springs, and the original single spring is easy to cause shell-taking failure.
The 6.8×43mm special bullet originated from the old 0.30-inch Remington bullet. The length of the shell is obviously short, but the diameter of the bottom and edge of the shell is basically the same as that of the early shell. At present, 7.45g competition warhead is used, but all-metal armored warhead and soft-pointed warhead will be put into production soon.
It should be pointed out that the ballistic performance of this 6.8 mm special bullet is almost the same as that of the British 0.280 inch bullet that has been used for 50 years. This is not to say that Remington copied the old-fashioned design, but that this old-fashioned bullet still has some merits.
Some trial-produced 6.8 mm special bullets have been tested by gelatin (simulating human muscle tissue) ballistics. In the test, this 6.8mm special bullet was fired from a barrel with a length of 368mm, and the initial velocity loss was only 15m/s, but the lethality of the weapon was better than that of the 5.56mmSS 109 bullet. The test shows that this 6.8 mm bullet is an excellent melee bullet for M4 carbine, which is suitable for military or law enforcement agencies.
Even for a barrel as short as 305mm, the muzzle kinetic energy can reach 1996 Joule, which is greater than that of a 7.62×39mm bullet with muzzle kinetic energy of 1975 Joule. If fired from a standard barrel with a length of 406mm, the muzzle kinetic energy reaches 234 1 joule. In the American official test, the average penetration depth of 45 rounds of ammunition to 100% gelatin is 399mm at100 m.
The average penetration thickness of this 6.8mm bullet is 178mm, which is measured by NIJ Ⅲ A bulletproof vest. M468 is well controlled in continuous firing, and the gun with silencer can control all shots within the perimeter of 25.4cm at 50m. Its muffler makes it unnecessary for the shooter to use earplugs when shooting.
When Remington Company launched the 6.8mm SPC bomb, Barrett Company took the lead in launching the AR- 15 rifle with this caliber, which was named M468 special carbine. At first, the M468 produced by Barrett Weapons Company was just an upper shell including the barrel. As long as the ordinary M 16/M4 is replaced by this upper shell, the 6.8mm SPC bullet can be fired. Then I just sold the whole gun.
Because the muzzle impulse of 6.8mmSPC bullet is greater than that of 5.56mm bullet, muzzle brake is installed. The interface with the muffler is a part of the air guide hoop, which is said to be a patented design of Barrett Company. When installing the muffler, first remove the knurled retaining ring, then screw on the muffler and lock the muffler in place with the spring lock key. When it is necessary to release, just press a button. It is said that the recoil of M468 is slightly less than that of 7.62×39mm unbarred AK rifle.
6.8mmSPC can directly use the 5.56mm magazine, but due to the large magazine diameter, a 30-round M 16 magazine can only hold 28 rounds of 6.8mm magazines. Therefore, the magazine capacity of M468 in the early performance elements provided by Barrett Company was 28 rounds, but recently this figure was updated to 30 rounds, because Barrett Company specially produced extended magazines.
Generally speaking, Barrett M468 carbine is characterized by portability, easy control, long range and good shooting accuracy, and its terminal efficiency is better than the current 5.56mm NATO bomb. However, because the US military is still only "interested" in the 6.8mm SPC bomb and has done some basic tests, there is no desire to further test and test the equipment.
So Barrett M468 carbine didn't receive a big order. Moreover, even if the US military decides to completely replace the 6.8mm SPC bomb, it is estimated that it is most likely that Colt or FN will provide the above example to modify the existing weapon. Barrett's production capacity may not give the military confidence to hand over all orders to them.