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Possibly strange question

Discussion in 'The Guns Galore Section' started by Oli, Jun 6, 2005.

  1. Oli

    Oli New Member

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    Could anyone tell me the outside diameter of a WII 75mm gun barrel, specifically French. I've got a decent side view (photo) of the Renault G1R from the 'net, and I'm running through my raster-to-vector software so that I can put it into a CAD package - and then scale it up to get dimensions. The only problem is that there's nothing, apart from the gun barrel to give me a reference as to scale/ size.
    I remember reading that a rifle barrel is about 33% larger than its bore, making a 75mm about 100mm outside, but does that percentage hold true for weapons other than rifles? And how much exactly is about 33%?
    Thanks in advance,
    Oli
     
  2. David Lehmann

    David Lehmann New Member

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    I don't really know ... but for example have a look at the thickness of the 75mm SA35 hull gun's barrel of the Renault B1bis :
     
  3. FNG phpbb3

    FNG phpbb3 New Member

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    If you tell me the caliber of the hull gun you could measure it a graphics program.

    FNG
     
  4. David Lehmann

    David Lehmann New Member

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    As I wrote, 75mm ;)
     
  5. Oli

    Oli New Member

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    Ouch!
    Thanks David. That looks to be considerably more than 100mm if the bore is 75. Which now makes me think that the photos showing the G1R mockup are fitted with the wrong gun
    The weapon supposedly for the G1R was, AFAIK, going to be the HV (Haut Vitesse/ High Velocity (nice that it has the same initials in English and French) APX, at about 570 metres/ sec, and there's a post on TankNet that suggests that G1R might have gone into service with an L/53 weapon firing 75/57 mm APCR.
    But the photo and what I've measured so far (assuming 100 barrel outside diameter) give reasonable dimensions for the vehicle (about 5 1/2 to 6 metres long and 2 1/4 metres high) but the barrel is extremely short - maybe not enough for 570 m/s firing Mle 1915 ammo (Char B1bis is 490 m/sec) I'd be looking for a 30%+ increase in barrel length over that ofChar B. And if the barrel is larger than 100mm that means that the whole vehicle is smaller!
    Thanks again for the photo,and will let you know how I get on with it.
    Oli
     
  6. Ricky

    Ricky New Member

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    Have you tried googling for a picture of the G1R that shows the end of the gun barrel? It might exist if you are lucky...
     
  7. Oli

    Oli New Member

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    I have one or two. :oops: Just looked at them and the barrel is much thinner.
    Photo from http://france1940.free.fr/armee/otdb1.html to give credit where it's due.
    Looks like the statements that the gun is "based on" mean "loosely based on".
    I'd still like an actual measurement if any one knows it though - confirmation is always a good idea.
    Oli
     
  8. David Lehmann

    David Lehmann New Member

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    Hello,

    THe 75mm SA35 L/17.1 fired theses shells :

    Obus de rupture Mle1910M (APHE)
    Caliber : 75x241R mm
    Weight of projectile : 6.400 kg (90g explosive)
    Length of projectile : 239.5mm
    V° = 475 m/s
    Penetration : 40mm /30° at 400m
    The APHE shell is intended to detonate once the armor has been penetrated. Because of the necessity for a hard point to APHE shells, the fuze is fitted into the base of the projectile. This fuze acts through inertia. As the shell passes up the barrel, either the shock of firing or the rapid rotation removes a safety device and arms the fuze. This fuze contains roughly a weight held by a spring. When the shell hits something hard, momentum throws the weight forward so it strikes the firing element of the fuze and thereby ignites the HE filler of the APHE shell.

    Obus explosif Mle1915 (HE)
    Caliber : 75x241R mm
    Weight of projectile : 5.550 kg (740g explosive)
    V° = 500 m/s
    Equipped with the long RYG Mle1921 fuze for better anti-personal efficiency. This long fuze explains probably why there were only 6 armed shells in the B1bis and 6 longer emplacements for them in the ammunition racks.

    The 75mm HE shells are able to destroy the armored cars, Panzer I and Panzer II and are very efficient at short range against the tracks and lower parts of the heavier tanks. The HE shell has a penetration of 17mm/30° even at 800m.

    Accuracy of the 75mm SA35 gun :
    10 shots at 400m : H+L = 30+28 = 58cm


    Concerning the Renault G1 tank :
    In 1936 a new program is launched to develop a "G" tank for the infantry. Somua, SEAM and Renault will propose prototypes or models. The initial requirement are a weight of about 20 tons, an armor of 50mm, a top speed of 50 km/h, a range of about 200 km and an armament consisting in a 47mm (75mm) gun mounted in a turret and 2 MGs. In fact the infantry wanted a kind of Somua S35 like the cavalry. The G1 tank would be lighter than the B1bis, easier to produce and cheaper to produce. At the same time, Germany started to study the Panzer III and the Panzer IV, armed respectively with a 37mm and a 75mm gun mounted in a turret.

    • For Somua the chassis is the one of the future Somua S40 with a dual armament, an APX4 turret with a 47mm SA35 gun and a 75mm hull gun. It is a kind of B1bis but weighting about 25 tons instead of 32 tons. The armor would reach 60mm, there is a 300hp engine (12 cylinders) allowing to reach 40 km/h and the hull gun as a traverse of 12°. These projects are not followed but will lead to the development of the Somua SAu40.

    • The second prototype is the G1P (P for Poniatowski) developed by SEAM. This project is also a dual tank, it will be stopped. The Germans will capture at least one prototype in 1940 according to photographic evidences.

    • Renault develops a different tank, with a modern chassis and all the armament in a new kind of turret. The turret will be equipped with a 47mm L/53 gun (V° = 840 m/s) and/or a 75mm gun (shortened 75mm Mle1897 barrel with a semi-automatic breech Mle1935 - V° = 555 m/s). The studies from Renault are more similar to the Panzer IV in Germany, the T34 in Russia or the future M4 Sherman in 1942, which will be partly inspired by French engineers detached in Washington in July 1940. The G1R would have been produced in September 1940 (the effective war against Germany was not expected before 1941) but the development was stopped in June 1940. The French in 1937/1939 also preferred a dual armament at this time, like the British for the first developments of the Churchill and the USA with the later M3 Grant for the USA. In May 1940, the combats proved that Renault was right with its 75mm gun mounted in the turret and such a tank would have been really useful. The USA will nonetheless develop the M3 Grant, arguing that it was too intricate to handle 75mm shells in a small turret. The British will cancel the planned mounting of a 3 inches (76.2mm) gun in the Chassis of the Churchill after Saint-Nazaire in 1941 and the first combats in North-Africa. The Renault G1R is armed with a 47mm SA37 L/53 gun or a 75mm gun based on the barrel of the 75mm Mle1897 field gun, both can be seen on the wooden models made by Renault. The anti-tank capacity is far better with the 47mm gun but the HE shells are more powerful for the 75mm guns. It is therefore planned to arm platoons of 3-5 tanks with 47mm and 75mm armed tanks. The 75mm gun would also have been able to fire the new Brandt 75/57mm sub-calibrated shells and Brandt HEAT shells.



    The 75mm Mle1897 (field gun) barrel is only a L/36.3 and fires a 75x350R shells.

    If you are refeering to a L/53 75mm guns, this was was developped as AT/AA gun by Scheider.
    Canon de 75mm L/53 TAZ Mle1939 (Schneider) (TAZ = triflèche tous azimuts)
    Caliber : 75x518R mm
    Barrel length : 4000 mm (3250 mm rifling)
    Battle-station weight : 2090 kg
    Rate of fire : 20 rpm
    Muzzle velocity : 700 m/s
    Traverse : 360°
    Elevation : 40°
    Maximum range : 13000 m (3000m in AA role)
    Penetration : 80mm at 1000m
    The 75mm Mle1939 had a 3-trails carriage for a 360° traverse and should have replaced all the 75mm AT guns (75mm Mle1897 and Mle1897/33 used in AT role, 75x350R mm) (and part of the 47mm Mle1937 AT guns probaly) at the divisional level but it did not enter in service before the armistice. This gun could have used the Brandt sub-calibrated 75/57mm shells and Brandt HEAT projectiles which are tested in 1940 to even increase a lot the AT capacity.


    Brandt new generation shells
    The studies led by Brandt in the 30's aimed to increase the initial velocity of the shells (without increasing of the chamber pressure) and also more generally to increase the penetration power of the shells. The French company Brandt developed series of sub-calibrated HVAP/APCR/APHC shells : 37/25mm, 75/57mm and also sub-calibrated projectiles for the 155mm and 203mm guns of the French navy. The other nations did not develop similar or equivalent systems before 1941/1942.
    The 37/25mm subcalibrated shell with a 20mm core was tested but could not enter in service before the armistice. The V° was 850 m/s and it had the same penetration capacity than the 25mm SA34/37 AT gun. The same 37/25mm subcalibrated shell was also planned to be used in the 25mm SA34/37 AT gun, reaching in that case a V° of 1150 m/s, but the barrels had to be modified. The most outstanding realization is probably the 75/57mm shell with a muzzle velocity of 900 m/s and a penetration of 90mm/35° at 1000m ... The 75mm Mle1897 and Mle1897/33 guns could have engaged and destroyed the German Panzer IVs at 2500m in May/June if such shells would have been available !
    Beside the sub-calibrated shells, Brandt also developed a 75mm HEAT shell at this time, using the patent of the Swiss Mohaupt. The tests took place in Bourges in 1940 and the results were that impressive that they were put in the secret immediately in order to avoid German capture.
    On 14th June 1940, the French war ministry authorized Brandt to give all these info to the USA and the United Kingdom, including the exploitation licence for the Mohaupt patent. The inventor, Henry Mohaupt, by the intermediary of the Brandt company filed for US patent on 10th February 1941 and it is kept secret on 7th March 1941. The sub-calibrated shells were used in the UK as basis to develop the APDS shells (armored piercing discarded sabot) issued from 1942/1943. The first AT guns using them were the 6 Pdr and 17 Pdr AT guns.

    Regards,

    David
     
  9. Ricky

    Ricky New Member

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    Dang.

    http://mailer.fsu.edu/~akirk/tanks/ is usually quite helpful, and does have pictures, but only contains these details (the tank is under 'other vehicles' in the French section)

    ---
    Renault GR-1

    Designed in 1936 as a replacement for the D2. The design was rejected in 1940.

    Specifications Crew ?
    Weight ?
    Dimensions ?
    Armor ?
    Armament 1 x 75mm
    Powerplant ?
    Performance 40kmh

    :angry:
     

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