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Old May 27, 2003, 15:23   #1
Eclipse
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Join Date: Aug 2000
Location: South Dakota
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WW2 era Australian .50 BMG design

Ran across this weapon description in google.com cache of a 404 web page. Describes a ww2 era MG developed in Australia. Anyone have more info or pictures of this design by Russell S. Robinson?

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The Best .50 Cal Machine Gun
that never entered service

Imagine firing a .50 caliber low recoil machine gun from the shoulder, sounds unbelievable doesn't it. Even more unbelievable when you learn that it was done in World War II in Australia and later in the United Kingdom not in America.

Take a shoulder fired .50 caliber semi auto rifle, several different .50 cal low recoil machine guns, a 9mm machine pistol the size of a Colt M1911A1 that has a cyclic rate of 600 rounds per minute with automatic ejection of empty magazines, a .30 caliber tank machine gun that had negligible gassing (filling the interior of the tank with propellant gases) plus a number of other designs and together they all add up to being the designs of a little known small arms designer named Russell S. Robinson.

Russell S. Robinson is not widely know outside the closed circles of small arms/ordnance designers, some non American military designers and serious students of modern small arms (like the author). In fact he doesn't even get a mention in the late Colonel Chinn's The Machine Gun unless you count the number of patents in his name in Volume 5. This is quite strange and one can't help but wonder why. Even here in Australia (yes the author is Australian) where a lot of his work was performed, little is known about Russ Robinson and his weapons.

Born in New Zealand in 1911, his family moved to Australia when he was 9, the family moved again, this time to the United States. Robinson was educated in the United States and graduated from the Massachusetts Institute of Technology (MIT) in 1932 as an aeronautical engineer, during that time designing and building his own aircraft. A member of Admiral Byrd's second expedition to the Antarctic from 1933 - 1935, he stayed on in his native New Zealand instead of returning with the expedition to the United States, where the Great Depression still ruled. Moving to Australia again, he designed garage equipment before moving to the United Kingdom to participate in the re-equipping of the Royal Air Force to meet the Luftwaffe threat. In the U.K. he worked for the Westland Aircraft co. and the Bristol Aeroplane Co.

After spending two years in the U.K., while still at Bristol, he joined the Civil Aviation Board as an aeronautical engineer. At that time the Nazis were releasing photographs and news describing the enormous production of aircraft and tanks for the purpose of intimidating their neighbors. The British press published this Nazi propaganda verbatim for the purpose of drawing public opinion away from the several peace-at-any-price groups. At the same time the government was keen to know the true German aircraft production, but the information was almost impossible to obtain as the Nazi security system was very capable and they were very rough on spies of any kind. Robinson's return to Australia offered one small opportunity.

He was schooled to judge the various clues by which production can be estimated and the was sent back to Australia via a tour of France, Holland, Germany and Italy. His cover in the Axis countries was as a specialist in aircraft nose wheel technology; the nose wheel was just coming into use at the time. He was not allowed to take notes or photos of any kind so when he visited such plants as Heinkel, Messerschmitt, Junkers and Focke Wulf, he talked about nose wheels but made mental estimates of the production that was going on. This was passed onto the British Air Attaché each time he returned to Berlin.

Finally, on reaching the Civil Aviation Board HQ, then at Victoria Barracks, Melbourne, Robinson worked on civil aircraft engineering problems. Upon the outbreak of war in 1939 he was sent to Sydney to design and supervise work on conversion of QANTAS Empire Flying Boats to reconnaissance bombers. This involved doubling fuel capacity, as well as the conversion of the DH84 to Wireless Gunner trainers, and the conversion of the DH86 to Hospital Aircraft - a design that was adopted throughout the British Empire for that aircraft. He was commissioned in the Royal Australian Air Force (RAAF), the second oldest in the world, as an officer in June 1941, and was appointed the area technical officer, directorate of production, covering the states of New South Wales and Queensland.





Short Empire Flying Boat



De Haviland DH84 Dragon De Haviland DH86 Express


De Haviland DH86 Hospital Aircraft (conversion) in RAAF service

A major problem for the RAAF was the Japanese A6M Zero and its armament, which vastly out gunned the planes then in RAAF service. At the time RAAF aircraft were armed with .30 cal or .303 machine guns while the Zero had 20mm cannons plus machine guns. Desperate to counter the Zero, it was eventually decided that a .50 cal machine gun would be ideal. However, it was felt that the mounts in the RAAF aircraft would not be able to cope with the recoil of the.50 and there was insufficient volume in the weapons bays to fit the .50 cal mgs and ammunition. A lack of time led Flight Lieutenant Russell S. Robinson to propose and idea that he originally conceived while an undergraduate at MIT and which later became known as the Constant Reaction Gun (CRG).

On 11 May 1942 Robinson submitted to the Australian Army Inventions Directorate (AID) a proposal to reduce recoil in a machine gun. Following a review, he was given permission by the RAAF to develop a demonstrator gun, now known as a proof-of-concept gun. This was to be done in his own time but using the facilities available to him by a number of contractors. The gun was somewhat crudely made due to a lack of adequate facilities, and made largely of welded mild steel, so that its reliability was irregular at best. It was the only gun he built that never worked properly during development and test firing, but which fired faultlessly during official demonstrations. However it did prove the feasibility of the Constant Reaction Principle, or as termed but the Australian AID, the Constant Recoil Principle.

First CRG described

Using a converted Browning .50 cal barrel, with a central bearing instead of the usual forward bearing, the gun had a simple receiver/stock formed as a deep channel. With simple bearings to support the barrel and cams to operate the locking piece and the primary extraction toggles, stops were bolted inside to limit barrel travel. A shoulder butt was welded to the rear and two hand grips bolted on to the underside of the receiver stock. Barrel movement was 3.5 inches with a simple barrel extension incorporating bolt locking-piece guides and wings for support of the bolt lever and hammer mechanisms. A very stiff V-spring was used for the driving spring.

The weight of the gun complete was 18 pounds with a 36 inch, 9 pound barrel, and when fired, reduced recoil to that of a .303 Lee Enfield No1 MkIII* SMLE rifle, although the muzzle energy is six times as great.





S.R. Model 2 .50 cal rifle disassembled


S.R. Model 2 .50 cal rifle partially assembled

The .50 cal barrel and ammunition were supplied by Ordnance Branch, U.S. HQ Sydney, and later on, more barrels and ammunition were again supplied by U.S. personnel. While U.S. Ordnance personnel were very helpful in Australian, Robinson's later experiences with the U.S. Army Ordnance establishment in Washington and Springfield under Col. Rene Studler were not as friendly probably because he invented a better, smaller .50 cal machine gun that out performed the .50 cal M2HB.

The first gun, known as the S.R. Model 2 .50 cal rifle, was first demonstrated before the RAAF and American and Australian Army personnel in New South Wales. The most important demonstration was on 6 October 1942 before high ranking Australian officer at Fort Gellibrand, near Melbourne, Victoria. The Gun had a nine-round magazine but only six rounds could be reliably fired. Numerous four and six round bursts were fired for the shoulder of a standing man while much of the weight of the gun was supported on a friction-free post.

Following the successful demonstration of the S.R. Model 2, the proposal for a new .50 cal machine gun was referred to the Army New Munitions Committee. Following their favorable comments, Robinson was placed on the RAAF Reserve list to enable him to dedicate full time and resources on the development of new guns and the Constant Reaction Principle, and the AID placed and order on his firm, the Shepherd Robinson Arms Development Co. that he had just formed (Shepherd being Robinson's middle name).

The AID also placed an order in February 1943 with the Munitions Annex, Slazenger's (Aust) Pty Ltd for the manufacture of a single prototype and spares for the drawings supplied by Robinson. By June 1943, 130 drawings had be supplied to Slazenger's and the prototype was completed for trials in October 1943. This weapon was to be known as the S.R. Model 5 and was Robinson's first attempt at a belt-fed machine gun. All drawings, fully toleranced, were prepared. It took him and two assistants only three and a half months to complete.





The Model 5 .50 cal machine gun completely disassembled

With a total weight of only 31 pounds, including the 10 pound barrel, the S.R. Model 5 could be made to feed from the left or right without tools, a and cyclic rate of 650 rounds per minute.

Compared to the .50 cal Browning aircraft gun, the S.R. Model 5 offered a number of advantages, such as a reduction in recoil force as well as weight and length of breech casing and increased effective range. The Model 5, having less than half the weight of the .50 cal Browning with the same barrel weight, created considerable interest in Australia. Tests on a stiff mounted reaction tester indicated only 15% of the peak trunnion reaction, but what was amazing was that the gun had a much shorter inboard length than any .30 cal machine gun then available.

RAAF issues requirement

The RAAF requirement was very interesting;

Ammo: Standard metal linked U.S. Caliber .50 ball

Muzzle Velocity: Not less than U.S. Standard

Inboard length: Not to exceed the Vickers .303 K gun

Weight: Approximately the same as the Vickers K gun

Trunnion Reaction: Not greater than the Browning .30 Aircraft machine gun

Barrel Length and weight same as the .50 cal Browning (36 inches and 10 pounds)

Cyclic rate: 650-700 rpm.

Feed: Left or Right

Manufacture: No exotic materials or processes

Although there were problems with the Model 5 (springs), it was agreed that funding be continued for the redesign.

This weapon was called the S.R. Model 14 .50 cal machine gun. Two versions where designed: an aircraft gun and a land service version for the Australian Army. The former had a 10 pound barrel while the later had two quick-change barrel weights: a 30 pound barrel with a rate of 350 rpm and a 23 pound barrel with a rate of 450 rpm. Again the complete gun weight was reduced compared to the Browning: 34 pounds for the aircraft gun and 48 pounds for the land service gun. Reduction in recoil force allowed for the land service gun, with a shortened barrel and modified trigger mechanism, to be fired form the shoulder.

The "demonstrator version, as Robinson called it, was use to demonstrate the effectiveness of the design to reduce recoil. Anyone seeing a .50 cal machine gun being fired from the shoulder in burst fire mode soon realized that such a gun was different.



Russell Robinson firing the "demonstrator" S.R. Model 14 .50 cal




Somewhat blurred, this photo, one of only four in existence shows the Model 14 demonstrator being fired in Australian during WWII


In an ironic twist, the Australian Army in 1996 called for tenders for a number of quick-change heavy barrel .50 cal Machine guns, not realizing that they could have had such a weapon in service for 50 year if only they had adopted the Model 14. Worse still the tender lapsed as no suitable guns were submitted and lack of investigation by the Australian Army has left the Model 14 in obscurity.
In January 1945, Robinson returned to the U.K. where there was great interest in CRG and principle. Visiting Cheshunt, where the design and development groups from the bombed-out Enfield Small Arms Factory were stationed. Upon meeting the assistant chief engineer for armament design/small arms and showing him the blue-prints for the S.R. Model 14, he was advised that the CEAD proposed to build a quantity of the Model 14 as soon as possible.

In six weeks, enough parts for six guns plus spares were built under high priority subcontract. These guns were assembled progressively. Each gun incorporated permanently, in new or modified parts, the alternations necessary during trials of its predecessor. Instead of using one gun with which to do all development work, as the resulting variable performance hopelessly confused later diagnoses of more obscure stoppages.

Robinson was soon back at work in Australia working on a redesign of the breech mechanism to cut down its weight and friction. The lack of energy, coupled with the breech mechanism's weight and friction was the reason for the failure of the Model 14 aircraft version to achieve a 1,000 rpm cyclic rate.





The model 14 on a U.S. .30 cal mount


The model 14 on field trials


The S.R. Model 14 aircraft version (top) the .50 cal Browning aircraft machine gun (bottom)

Some six aircraft guns were produced at the Royal Small Arms Factory, Enfield and 12 Land service guns were produced at the Small Arms Factory, Lithgow, New South Wales.


Constant Reaction in Action
The Constant reaction gun principle is a self powered F.O.O.B ( Firing out of battery) gun where the movement of the barrel is never interrupted during the firing of a burst. Accordingly, the unbalanced rearward reaction of the gun against mount is never interrupted...[and] if the driving spring has a flat rate reaction and the gun is designed to use a minimum of energy for reloading, then the trunnion reaction is relatively stead and free of surges.... it is very low and steady trunnion reaction that enables the C.R.G.. weapon to be so unusually compact and of light weight. The stresses in the receiver and major functioning components are small due to low barrel velocities.

A CRG is arranged so that the barrel, breech block, etc, can slide longitudinally between given limits with a spring (or other force) mechanism imposing a forward-directed driving force onto the barrel system. In the non-firing position, the barrel is held near its rear limit of travel by a sear.

When the sear is activated, the barrel is released, feeding and loading a cartridge are carried out while the barrel is still moving forward. The driving force is a substantially constant force across the entire normal movement range of the barrel and breech block. The force is such that it imparts to the moving mass (after a certain distance of travel) momentum equal to approximately one-half the total momentum of recoil (projectile plus gases).

Before the barrel reaches its front limit, the cartridge is fired, resulting in the forward movement of the barrel being stopped. At the same time, there is a rearward energy generated by the firing of the cartridge to move the barrel mass against the driving spring to its rear limit. During the recoil of the barrel, the breech is unlocked, extraction and ejection occur. The barrel reaches is rear limit with a clear chamber, and the next round is in position ready for loading.

While the barrel is moving , the spring's rearward pressure against the receiver is unaffected by the sear or any other part. This means that the movement of the receiver against the mount sis continuous and relatively steady. whole the barrel's free movement is never interrupted mechanically for reloading or any other purpose. This basic principle was use by Russell Robinson for most of his weapons, albiet with a number of variations depending upon the application and type of gun required or being designed.
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