6mm Optimum from the other side of the Iron Curtain
A prophet in his own country: 6mm Optimum from the other side of the Iron Curtain
Note: I'm no expert in Internal Ballistics or hand-loading. Please feel free to correct me.
IOTL, a meeting on the consideration of new foreign weapons chambered for a reduced power cartridge was held in the Technical Council of the People's Commissariat of Armaments (TS NKV) on July 15, 1943. Gunsmith designers, heads of the Special Design Bureau 44 (OKB-44, Kuntsevo, Moscow Region) and military specialists were invited to it. A representative of the Artillery Committee of the Main Artillery Directorate (Artcom GAU) demonstrated the German MKb.42 (H) automatic carbine, which fell into the hands of Soviet troops on the Volkhov front, and the American 7,62-mm self-loading carbine .30 M1 chambered for a pistol cartridge of increased power.
Thus, the meeting participants decided "to instruct OKB-44 to carry out calculations to select the optimal speed of the bullet and its most advantageous mass for calibers 5,6, 6,5 and 7,62 mm, as found in practice. The barrel length is 520 mm, and the average pressure is 3.000 kg / cm2 (2.942 bar). The bullet must have sufficient lethal force to incapacitate a person at a distance of 1.000 m. The task was urgent, but not entirely clear. The OKB-44 certificate from 1947 says: "By the time the new cartridge was designed, we had nothing ... No one knew what was required of the new cartridge. Only by the perseverance with which the 6,5 mm caliber was recommended, and based on subsequent events, it can be assumed that General Vladimir Grigorievich Fedorov (1874-1966) was behind this idea.
Back in 1939, he wrote: "The evolution of individual models of small arms can go to the rapprochement of two types - an assault rifle and a submachine gun based on the design of a new cartridge. The creation of one cartridge with a reduced aiming range for rifles and increased for submachine guns would solve the problem of creating a future weapon - powerful thanks to the adoption of automatism with an interpreter for single and continuous firing, light and compact due to the adoption of a cartridge with a smaller size, with a smaller caliber (6-6,25 mm) and with a sleeve without a rim. Bullets for such a cartridge were recommended light - with a transverse load (the ratio of the mass of the bullet to the cross-sectional area) - 18-20 g / cm2. The length of the barrel is about 520 mm. The shape of the bullet of the new cartridge was improved gradually. The lead-core bullet was designed without a rear cone and with a short head. The GAU approved this project of the cartridge for testing. In the future, the bullet model 1943 acquired a rear cone due to the development of a powder charge.
At this POD, General Fyodorov's zeal for 6,5mm caliber finally bore fruit. The committee no longer insisted existing fixtures be inherited where 7,62mm caliber should gain a competitive edge, but still required that the role 7,62×54mmR in long range should be assured by its substitute, which further disadvantaged an intermediate cartridge of 7,62mm caliber. A muzzle energy of 2.000 ft⋅lbf was found necessary.
They showed that in the caliber of 7,62 mm, in order to obtain a gain in weight and dimensions, it is necessary to reduce the range of a direct shot compared to a rifle cartridge to 20%. The 6,5mm reference (6,5mm Arisaka) proved unsuitable to drop horses or penetrate brick walls in combat range. As for the caliber of 5,6, they found difficulties in producing tracer or incendiary rounds, and keeping accuracy and lethality at long range without excessive bore erosion and exceeding chamber pressure limit.
With both rifles and submachine guns in mind, in 1944, a 6,5×42mm rimless cartridge came out of the blueprint. It has a long, sharp bullet of 33mm/1,30", 8 gram/123 gr with mild steel core, a highly tapered brass case that holds powder enough to generate Pm of 300MPa/43,5 kPsi (Pmmax <320MPa/46,4 KPsi) and drive the bullet to a muzzle velocity of 820m/s (2,700 fps) in a 610mm/24" barrel. Compared with 7,62×39mm, the shell is slightly extended to 42mm to accommodate a long bullet and more powder, and elongate the cartridge to 60mm, and the bullet is 28% more powerful (2.690J/1.984 ft⋅lbf) than history. The high ballistic coefficient (BC) of more than .5 allows the bullet remains supersonic at 1.000 meters.
At the target range, the inspectors from GAU observed that the bullet has a direct shooting range of more than 300 meters, tumbles greatly in soap target at 100 meters with Mosin's default twist of 1:9,45" creating horrible wounds before exiting the trunk of scapegoat's body, and penetrates both the outer and inner layer of M1 Helmet at 1.000 meters With recoil momentum 15% higher than 7,62×39, OKB-44 bureaucrats believed that the cartridge barely meets the requirement of controllability as a handheld automatic weapon, and that after WW2 there would be no pressing need to drop a horse in Motorized Warfare. The cartridge was finalized and put into production.
In the 1950s, the Soviets managed to master the process of producing bimetal and lacquered steel cases that withstood 300 MPa, thus soon all those shells were made of steel case; and with the maturity of Avtomat Kalashnikov family, VZ 58 and Type 81 family (named after the foundation of PLA of China on August 1st, 1927, rather than the year of production 1981), mass production in Eastern Bloc and China began. It has become the standard infantry cartridge until today and replaced the role of both 7,62×54mmR and 7,62×25mm.
Type 81 automatic carbine in this timeline has a 20-inch barrel. The LMG version has a barrel of 24 inches.
Sequel:
1. The Soviets dumped all 7,62×54mmR and 7,62×25mm stuff in the Korean War and First Indochina War: that's how they got rid of the burden of history.
2. Just after the development of the 6,5mm caliber, a 9mm machinegun and sniper cartridge trying to replace both 7,62mm MMG and 12,7mm HMG round was put into development with the bullet weight of 16g and energy of 5.000 ft⋅lbf for long range (2.500m+), accurate shooting and penetrating light armors about 25mm (Hey, it has a bullet length of 45mm compared with 57,9mm of .50 Cal.), which saw limited success on a sniper rifle named Dragunov, and a mountain infantry machinegun named PK. But as the heritage of the 9mm cartridge, the 16g AP bullet was adopted by a subsonic cartridge with a parent case of 6,5×42mm that serves as a silenced AK variant.
3. The trembling phenomenon found in the 6,5mm cartridge contributed to the development of a 5,6mm caliber 3-gram Mach 3 SCHV cartridge that was first tested on an M2 clone and then adopted by the AK platform for simplification of training, where muzzle energy has been limited to 1.000 ft⋅lbf and muzzle velocity has been reduced. The new AK variant was first adopted as PDW for the service forces and then as the standard primary weapon of motorized infantry.
4. IOTL in Afghanistan, a wild-cat cartridge of 6,5mm was, indeed, created by a Soviet armorer Aleksandrom Shevchenko. Amazing, isn't it?
www.kalashnikov.ru
Note: I'm no expert in Internal Ballistics or hand-loading. Please feel free to correct me.
IOTL, a meeting on the consideration of new foreign weapons chambered for a reduced power cartridge was held in the Technical Council of the People's Commissariat of Armaments (TS NKV) on July 15, 1943. Gunsmith designers, heads of the Special Design Bureau 44 (OKB-44, Kuntsevo, Moscow Region) and military specialists were invited to it. A representative of the Artillery Committee of the Main Artillery Directorate (Artcom GAU) demonstrated the German MKb.42 (H) automatic carbine, which fell into the hands of Soviet troops on the Volkhov front, and the American 7,62-mm self-loading carbine .30 M1 chambered for a pistol cartridge of increased power.
Thus, the meeting participants decided "to instruct OKB-44 to carry out calculations to select the optimal speed of the bullet and its most advantageous mass for calibers 5,6, 6,5 and 7,62 mm, as found in practice. The barrel length is 520 mm, and the average pressure is 3.000 kg / cm2 (2.942 bar). The bullet must have sufficient lethal force to incapacitate a person at a distance of 1.000 m. The task was urgent, but not entirely clear. The OKB-44 certificate from 1947 says: "By the time the new cartridge was designed, we had nothing ... No one knew what was required of the new cartridge. Only by the perseverance with which the 6,5 mm caliber was recommended, and based on subsequent events, it can be assumed that General Vladimir Grigorievich Fedorov (1874-1966) was behind this idea.
Back in 1939, he wrote: "The evolution of individual models of small arms can go to the rapprochement of two types - an assault rifle and a submachine gun based on the design of a new cartridge. The creation of one cartridge with a reduced aiming range for rifles and increased for submachine guns would solve the problem of creating a future weapon - powerful thanks to the adoption of automatism with an interpreter for single and continuous firing, light and compact due to the adoption of a cartridge with a smaller size, with a smaller caliber (6-6,25 mm) and with a sleeve without a rim. Bullets for such a cartridge were recommended light - with a transverse load (the ratio of the mass of the bullet to the cross-sectional area) - 18-20 g / cm2. The length of the barrel is about 520 mm. The shape of the bullet of the new cartridge was improved gradually. The lead-core bullet was designed without a rear cone and with a short head. The GAU approved this project of the cartridge for testing. In the future, the bullet model 1943 acquired a rear cone due to the development of a powder charge.
Промежуточный патрон 7,62x39 мм образца 1943 г. (СССР) - RUFOR.ORG
Промежуточный патрон 7,62x39 мм образца 1943 г. (СССР) Патроны
37.143.9.186
At this POD, General Fyodorov's zeal for 6,5mm caliber finally bore fruit. The committee no longer insisted existing fixtures be inherited where 7,62mm caliber should gain a competitive edge, but still required that the role 7,62×54mmR in long range should be assured by its substitute, which further disadvantaged an intermediate cartridge of 7,62mm caliber. A muzzle energy of 2.000 ft⋅lbf was found necessary.
They showed that in the caliber of 7,62 mm, in order to obtain a gain in weight and dimensions, it is necessary to reduce the range of a direct shot compared to a rifle cartridge to 20%. The 6,5mm reference (6,5mm Arisaka) proved unsuitable to drop horses or penetrate brick walls in combat range. As for the caliber of 5,6, they found difficulties in producing tracer or incendiary rounds, and keeping accuracy and lethality at long range without excessive bore erosion and exceeding chamber pressure limit.
With both rifles and submachine guns in mind, in 1944, a 6,5×42mm rimless cartridge came out of the blueprint. It has a long, sharp bullet of 33mm/1,30", 8 gram/123 gr with mild steel core, a highly tapered brass case that holds powder enough to generate Pm of 300MPa/43,5 kPsi (Pmmax <320MPa/46,4 KPsi) and drive the bullet to a muzzle velocity of 820m/s (2,700 fps) in a 610mm/24" barrel. Compared with 7,62×39mm, the shell is slightly extended to 42mm to accommodate a long bullet and more powder, and elongate the cartridge to 60mm, and the bullet is 28% more powerful (2.690J/1.984 ft⋅lbf) than history. The high ballistic coefficient (BC) of more than .5 allows the bullet remains supersonic at 1.000 meters.
At the target range, the inspectors from GAU observed that the bullet has a direct shooting range of more than 300 meters, tumbles greatly in soap target at 100 meters with Mosin's default twist of 1:9,45" creating horrible wounds before exiting the trunk of scapegoat's body, and penetrates both the outer and inner layer of M1 Helmet at 1.000 meters With recoil momentum 15% higher than 7,62×39, OKB-44 bureaucrats believed that the cartridge barely meets the requirement of controllability as a handheld automatic weapon, and that after WW2 there would be no pressing need to drop a horse in Motorized Warfare. The cartridge was finalized and put into production.
Greenhill Formula {\displaystyle {\text{twist}}={\frac {CD^{2}}{L}}\times {\sqrt {\frac {\mathrm {SG} }{10.9}}}} 150*0.260*0.260/1.3=7.8"<<9.45"
The 9mm Parabellum fired from pistols will be stopped at the inner layer of M1 Helmet; though with the same terminal energy, it would make it with doubled sectional density (same bullet weight, less than half cross-sectional area) and mild steel core, I guess.
The 9mm Parabellum fired from pistols will be stopped at the inner layer of M1 Helmet; though with the same terminal energy, it would make it with doubled sectional density (same bullet weight, less than half cross-sectional area) and mild steel core, I guess.
In the 1950s, the Soviets managed to master the process of producing bimetal and lacquered steel cases that withstood 300 MPa, thus soon all those shells were made of steel case; and with the maturity of Avtomat Kalashnikov family, VZ 58 and Type 81 family (named after the foundation of PLA of China on August 1st, 1927, rather than the year of production 1981), mass production in Eastern Bloc and China began. It has become the standard infantry cartridge until today and replaced the role of both 7,62×54mmR and 7,62×25mm.
Type 81 automatic carbine in this timeline has a 20-inch barrel. The LMG version has a barrel of 24 inches.
Sequel:
1. The Soviets dumped all 7,62×54mmR and 7,62×25mm stuff in the Korean War and First Indochina War: that's how they got rid of the burden of history.
2. Just after the development of the 6,5mm caliber, a 9mm machinegun and sniper cartridge trying to replace both 7,62mm MMG and 12,7mm HMG round was put into development with the bullet weight of 16g and energy of 5.000 ft⋅lbf for long range (2.500m+), accurate shooting and penetrating light armors about 25mm (Hey, it has a bullet length of 45mm compared with 57,9mm of .50 Cal.), which saw limited success on a sniper rifle named Dragunov, and a mountain infantry machinegun named PK. But as the heritage of the 9mm cartridge, the 16g AP bullet was adopted by a subsonic cartridge with a parent case of 6,5×42mm that serves as a silenced AK variant.
3. The trembling phenomenon found in the 6,5mm cartridge contributed to the development of a 5,6mm caliber 3-gram Mach 3 SCHV cartridge that was first tested on an M2 clone and then adopted by the AK platform for simplification of training, where muzzle energy has been limited to 1.000 ft⋅lbf and muzzle velocity has been reduced. The new AK variant was first adopted as PDW for the service forces and then as the standard primary weapon of motorized infantry.
4. IOTL in Afghanistan, a wild-cat cartridge of 6,5mm was, indeed, created by a Soviet armorer Aleksandrom Shevchenko. Amazing, isn't it?
Родом из СССР? Неожиданная история патрона 6,5х38 Grendel | Оружейный журнал «КАЛАШНИКОВ»
Разработчики данного, более мощного по сравнению с боеприпасом калибра 5,56×45, патрона взяли за основу гильзу советского 7,62-мм автоматного патрона (7,62×39), переобжав дульце под пулю диаметром 6,5 мм. Конечно, если вдаваться в детали, то за «гренделем» торчат уши и советского спортивного...
www.kalashnikov.ru
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