pzgr40
Well-Known Member
Cutaway model of a 75mm M310B1 shaped charge shell for the M20 Recoilles rifle. This Rifle was placed on the M1917A1 tripod, which was originally meant for the browning machine gun. The M20 RR was taken into service in March 1945 and was to late for the war in Europe, but was used in limited numbers in the Pacific theatre. The M20 was exstensively used in the Korean war, where it was used against field fortifications and pillboxes. After the Korean war the recoiless rifle was replaced by guided missiles, which were more accurate and lighter.
The advantage of the Recoiless rifle is that it is light and easily transportable, the disadvantage is the reduced range and the backblast, which will give away the firing position from far away. Exept for the M1917 machine gun tripod, the M20 was also mounted on jeeps. An interesting combination was the Italian Vespa ABMA 150 Tap scooter which had the cannon incorperated along the frame, and was meant for paratroopers. The gun was however only transported with the scooter, and had to be taken out to place it in firing position.
Today the M20 recoiless rifle is used only by the US national forrest service as an anti avalanche system.
The working principal of the M20 Recoilless rifle can simply be described as “weight of gas from breech X speed of gas = weight of projectile X speed of projectile”. As long as this is in balance, the weapon is recoilless.
The shell case is perforated with 922 holes to let the gas vent afterward through the perforated breech block, the driving band of the projectile is pre-engraved as to lose no energy to rifling of the driving belt. Another reason for using pre-engraved driving belts is to prevent the pressure in the chamber from rising too high, as the recoilless rifle is also quite a thin walled light weapon . The absence of a recoil system also greatly reduces the weight of the weapon.
There are four types of shells available : the M309A1 High explosive sheel, the M310A1 HEAT shell,
the M311A1 Smoke (Phospor) and the Drill cartridge M38.
The projectile consists of a releatievly thin walled steel projectile with a copper cone in the upper part. The cone is locked up by a threaded ring with a steel nose cone brassed over the threaded ring.
Weight complete cartridge : 9,5 kg
Weight projectile with fuze : 6 kg
Length complete cartridge : 73,5cm
Length projectile : 40,5cm
Length shellcase : 40,5cm
The projectile is filled with 0,45 kg Pentolite 50/50 or 0,45 kg Comp.B
Vo is 305 mtrs/sec
Max range : 6350 mtrs
Penetration : 100 mm bij 90 graden.
The shaped charge projetile is ignited with the base fuze BD M62.
The fuze consists of a two part steel fuze body (1). The lower part houses the inertia weight (2) which is kept in the aft position by two steel pins (7) on springs. The firing pin is placed on a centrifugal rotor (3) with the firing pin rotated away from the detonator (8) in safe position. Two opposite placed centrifugal weights (5) on springs fixate the rotor (3) in safe position. The two centrifugal weights (5) are locked up by a brass ring (6) pressed over the inertia weight (2).
When the projectile is fired, the two centrifugal weights (5) are thrown outward, releasing the rotor (3). The rotor will rotate over it’s shaft (4, blue), rotating the firing pin in line with the detonator (8). Upon impact, the inertia weight (2) is swung forward, overcomming the two pins (7) on the spring, pressing the firing pin into the detonator (8).
In the drilled hole (11) between the detonator (9) and the booster charge (12) another centrifugal safety is placed. This consists of a slider (9), pushed inward by a spring (10). Before firing this locks the channel between the detonator (8) and the booster (12). Upon firing inertia keeps the slider forced inward -due to the downward angle of the hole-, but when acceleration decreases the centrifugal force throws the slider outward -riding it’s spring-, opening the hole for the flame of the detonator.
The M309B1 high explosive shell is described in this posting : 'M309A1 High Explosive shell for the M20 recoilless rifle, USA'.
Regards, DJH
The advantage of the Recoiless rifle is that it is light and easily transportable, the disadvantage is the reduced range and the backblast, which will give away the firing position from far away. Exept for the M1917 machine gun tripod, the M20 was also mounted on jeeps. An interesting combination was the Italian Vespa ABMA 150 Tap scooter which had the cannon incorperated along the frame, and was meant for paratroopers. The gun was however only transported with the scooter, and had to be taken out to place it in firing position.
Today the M20 recoiless rifle is used only by the US national forrest service as an anti avalanche system.
The working principal of the M20 Recoilless rifle can simply be described as “weight of gas from breech X speed of gas = weight of projectile X speed of projectile”. As long as this is in balance, the weapon is recoilless.
The shell case is perforated with 922 holes to let the gas vent afterward through the perforated breech block, the driving band of the projectile is pre-engraved as to lose no energy to rifling of the driving belt. Another reason for using pre-engraved driving belts is to prevent the pressure in the chamber from rising too high, as the recoilless rifle is also quite a thin walled light weapon . The absence of a recoil system also greatly reduces the weight of the weapon.
There are four types of shells available : the M309A1 High explosive sheel, the M310A1 HEAT shell,
the M311A1 Smoke (Phospor) and the Drill cartridge M38.
The projectile consists of a releatievly thin walled steel projectile with a copper cone in the upper part. The cone is locked up by a threaded ring with a steel nose cone brassed over the threaded ring.
Weight complete cartridge : 9,5 kg
Weight projectile with fuze : 6 kg
Length complete cartridge : 73,5cm
Length projectile : 40,5cm
Length shellcase : 40,5cm
The projectile is filled with 0,45 kg Pentolite 50/50 or 0,45 kg Comp.B
Vo is 305 mtrs/sec
Max range : 6350 mtrs
Penetration : 100 mm bij 90 graden.
The shaped charge projetile is ignited with the base fuze BD M62.
The fuze consists of a two part steel fuze body (1). The lower part houses the inertia weight (2) which is kept in the aft position by two steel pins (7) on springs. The firing pin is placed on a centrifugal rotor (3) with the firing pin rotated away from the detonator (8) in safe position. Two opposite placed centrifugal weights (5) on springs fixate the rotor (3) in safe position. The two centrifugal weights (5) are locked up by a brass ring (6) pressed over the inertia weight (2).
When the projectile is fired, the two centrifugal weights (5) are thrown outward, releasing the rotor (3). The rotor will rotate over it’s shaft (4, blue), rotating the firing pin in line with the detonator (8). Upon impact, the inertia weight (2) is swung forward, overcomming the two pins (7) on the spring, pressing the firing pin into the detonator (8).
In the drilled hole (11) between the detonator (9) and the booster charge (12) another centrifugal safety is placed. This consists of a slider (9), pushed inward by a spring (10). Before firing this locks the channel between the detonator (8) and the booster (12). Upon firing inertia keeps the slider forced inward -due to the downward angle of the hole-, but when acceleration decreases the centrifugal force throws the slider outward -riding it’s spring-, opening the hole for the flame of the detonator.
The M309B1 high explosive shell is described in this posting : 'M309A1 High Explosive shell for the M20 recoilless rifle, USA'.
Regards, DJH
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