From the mid-forties, gunsmiths of Spain studied the problems of promising ammunition for rifle rifles. weapons, including intermediate class ammunition. In particular, the attention of experts was attracted by the German cartridge 7,92х33 mm Kurz, which had certain advantages over other products. Subsequently, several own ammunition of a similar purpose were created, markedly different from the German product.
One of the participants in the program of studying and creating cartridges was Lieutenant Colonel Joaquín de la Calzada-Bayo, who worked at the arsenal of La Coruña. Until a certain time, he was engaged only in the subject of cartridges, but in the early fifties he decided to develop his own version of the weapon for existing or serial ammunition. By the beginning of 1951, the officer identified the main points of the future project. In March, project works started, and in June a full-fledged project was presented.
According to known data, a promising model of small arms received the name "automatic carbine CB-51". The letters in the official designation were abbreviations of the name of the designer, and the numbers indicated the year the project was created. Interestingly, a different name was present on the receiver of the prototypes. They were designated as Fusil Asalto - "Assault Rifle". Subsequently, including after the creation of new modifications of weapons, such a designation has not changed. Samples of two models, created in the framework of one project, were proposed to be distinguished from each other, indicating along with the name of the weapon the type of cartridge.
It should be noted that in the same 1951 year, H. De La Calzada-Bayo developed at least one more sample of small arms, also designated CB-51. It was a self-loading rifle of the "traditional" type with developed wooden fittings, which also used the German cartridge 7,92x33 mm "Kurz". Using one designation for multiple samples can be confusing, but it is not too difficult to avoid.
Known information about the CB-51 project suggests that when it was created, H. De La Calzada-Bayo carefully studied some foreign developments and also borrowed certain ideas and solutions. In particular, the appearance, layout, and other features of the new Spanish weapon forced us to recall the German "assault rifles" of the final period of the war.
According to known data, the CB-51 rifle was supposed to be equipped with a gas engine that controls the movement of the bolt. The type of locking system is unknown. It was proposed to use a detachable receiver box consisting of a pair of large units and equipped with means for installing a magazine, mounting a butt, etc. Curiously, in terms of overall layout and ergonomics, the product of Lieutenant Colonel Kalsada-Bayo resembled both older rifles and the latest automata.
The main element of the rifle was a relatively large receiver, consisting of two main parts. Like some other systems of that time, the upper part of the box had fastenings for the barrel and the gas piston tube, and was also equipped with guides for the bolt and return spring. At the same time, unlike similar samples, the receiving device of the store was part of the upper “receiver”. The lower element of the receiver differed in smaller sizes and other sections. In it, first of all, were placed the details of the firing mechanism. The back of this unit formed a glass of complex shape, worn on the top element of the receiver.
In the front wall of the receiver fixed trunk and some other details. The CB-51 rifle received a relatively long rifled 7,92 mm caliber barrel with a cartridge chamber under the 33-mm sleeve. In the area of the chamber on the outer surface of the trunk there was a radiator with several transverse rings. A significant part of the trunk, with the exception of a small area at the barrel, was under the protective cover. The latter was a tube with several rows of longitudinal holes for the supply of air. The front of the casing was connected to the body of the flue gas assembly. The gas piston was placed above the barrel and was located in a longitudinal tube of polygonal cross section.
The layout of the automation units was traditional for systems with a gas engine. Inside the upper part of the receiver was placed a movable frame with the required configuration of the shutter. How exactly was organized locking the barrel before the shot - is unknown. Information on the application of the developments in the German project StG 44 suggests that the gate will be locked with a bias, but any other scheme could be used with equal probability. Inside the gate was placed a movable drummer, the management of which was assigned to the existing trigger. For cocking, it was proposed to use the bolt handle, which was brought out through a groove in the right wall of the receiver.
An interesting feature of the CB-51 rifle is the relatively short return spring. Unlike the German designers, H. De La Calsada-Bayo managed to fit this detail into the dimensions of the receiver, which, among other things, made it possible to optimize the design of the butt and bring the ergonomics of the weapon into the desired look.
In the back of the receiver fits the trigger mechanism, built, probably, according to the Kurk scheme. For fire control, a traditional trigger was used. Blocking the trigger or selecting its mode was carried out using the flag of the translator of the fire, which was displayed on the left side of the box, directly in front of the trigger guard. Depending on his position, the lever blocked the trigger, provided fire bursts or automatic fire. It should be noted that the trigger bracket was located almost at the level of the rear cover of the receiver - further than on foreign weapons of this class. This arrangement was due to the special ergonomics of the weapon.
Ammunition was supposed to be stored in detachable stores on 30 cartridges. According to various sources, such a store was either based on the German design, or completely repeated it without any noticeable changes. The magazine was placed in the receiving shaft of the receiver and secured in place with the help of the rear latch. For the ejection of the liners a small window was used on the right side of the receiver. The window was covered with a spring-loaded lid that protected the inside of the rifle from contamination.
The weapon received an open mechanical sight. Over the muzzle of the trunk was fixed triangular stand with front sight and its protective ring. At the level of the mine shop and the shutter on the receiver was a mechanical sight with the ability to adjust the range and making side corrections.
The product was proposed to equip a fairly simple fittings. Under the rear part of the barrel casing, a small forearm was fixed, made in the form of a relatively short wooden lining. This detail partially covered the trunk housing, leaving its upper openings open. Also, the CB-51 project provided for the use of a rifle butt type with a narrowed neck with a pistol protrusion. It was a similar butt, used together with the pistol grip traditional for automatic machines, that led to the need to move the trigger back. The rear surface of the butt was equipped with a metal back plate. On the left, on the gas discharge unit and on the butt, there were swivels for the belt.
Depending on the situation, the shooter could not only fire, but also go in bayonet. Knife-type blade was proposed to fix with a ring and a lock. The first was worn on the muzzle of the trunk, while the second was engaged with the tide, located under the gas outlet block.
As far as is known, the CB-51 rifle under the German cartridge 7,92x33 mm Kurz was the base representative of its family. By varying the basic components and assemblies of the lieutenant column De La Calzada-Bayo, he soon developed several new automatic rifles. The first version of the modernization of the rifle was created already in 1951 year and provided for a minimal revision of the original design with the aim of using a different ammunition.
Rifle arr. 1951 of the second type was supposed to use the original Spanish cartridge 7,92x40 mm, developed with the participation of H. De La Calsada-Bayo. This ammunition differed from the German longer, due to the increased dimensions of the liner and bullet. For this reason, the original design had to be significantly improved. The second rifle should have different proportions, be equipped with springs with other characteristics, etc.
The new rifle received a slightly longer barrel with an enlarged chamber. In addition, the front receiver section was extended, which included the store receiver. The use of a longer shutter led to the need for some reworking of other internal mechanisms. A new box magazine was created with the capacity of all 20 cartridges. Apparently, the reduction of ammunition needed to maintain an acceptable mass of weapons in combat condition.
All other components and assemblies of the rifle that did not interact with the new ammunition remained without noticeable changes. As a result, the automatic rifle chambered for the 7,92x40 mm was significantly longer and heavier than the base model, but it also had to show higher firing characteristics. Thus, due to a lighter bullet, it was planned to obtain a firing range of up to 1000 m with a sharp reduction in recoil compared to the Kurtz cartridge 7,92х33 mm.
The development of two promising small arms projects for German and Spanish intermediate cartridges ended in the summer of the year 1951. Soon the arsenal in La Coruna produced several prototypes of such rifles needed for factory testing. After preliminary checks aimed at identifying and correcting existing shortcomings, rifles were to be tested in the interests of the Spanish military department.
10 weapons and a certain amount of ammunition were ordered for this test phase. Unfortunately, there is no information about the proportions of the two types of rifles in the general order. It can be assumed that for testing produced several products of each type. To carry out all necessary checks, a customer could require at least several thousand 7,92x33 mm and 7,92x40 mm cartridges.
For a number of reasons, the production of an experimental batch of automatic rifles designed by Kalsada-Bayo and ammunition for them was noticeably delayed. It was possible to start new firing only with a noticeable delay. At the same time, the tests were noticeably delayed and continued until December 1952. One of the main reasons for the shift in the timing of work turned out to be problems with the release of German-style cartridges. The cartridge plant in the city of Palencia did not cope with the tasks assigned to it and did not have time to simultaneously produce a significant number of ammunition for the army and for experimental work.
For several months, the problem with the supply of ammunition was partially resolved, but the changes in the situation were not significant. Specialists from industry and the military together carried out part of the required tests, and the shortage of cartridges prevented some necessary tests from being carried out. Nevertheless, even in such a situation, the military were able to draw certain conclusions, and also to issue to the designers a list of recommendations regarding the further development of small arms.
During the tests of two new automatic rifles CB-51, it turned out that both new intermediate cartridges do not allow to obtain the desired characteristics. Rifles showed the required range of fire in 1000 m, but the fighting qualities of bullets at such distances left much to be desired. Also, probably, starting from a certain range, serious problems could appear with the accuracy and accuracy of fire.
In general, the rifles of the two models left an ambiguous impression. They could be considered very successful from a technical point of view, but they did not show the desired combat characteristics. Thus, with all its advantages, such weapons were of no interest to the army and therefore could not count on getting into the troops. However, the command did not refuse to develop Joaquín de la Calzada-Bayo. The designer was recommended to use a more powerful cartridge capable of giving the weapon the required characteristics.
The tests of a dozen CB-51 rifles ended at the end of the 1952 year. By this time, designers from La Coruna, taking into account the known results of inspections, began to develop a new rifle, based on the existing design. The result of the new work was the appearance of the automatic rifle CB-52, using the original cartridge 7,95х51 mm. At the turn of 1952 and 1953, the Spanish military were able to test this weapon at a shooting range and determine its real prospects.
It is known that in the 1951, the arsenal of La Coruna collected only ten CB-51 rifles of two modifications, using different cartridges. These products were used in tests and could not interest a potential customer. After refusing to adopt the fate of the prototypes was sealed. Probably the vast majority of finished products were sent to the smelting as superfluous. According to reports, after the end of the tests, only two CB-21 rifles were retained: one for the German cartridge and one for the Spanish. Currently, both prototypes are kept in the military history museum of the Museo Histórico Militar de A Coruña.
The aim of the CB-51 project was to create a promising automatic rifle with fairly high performance. To obtain the desired capabilities, it was proposed to use foreign and own cartridges, but it was not possible to fully solve the tasks posed. As a result, two CB-51 rifles were abandoned. However, the work did not stop, and soon the Spanish designers presented a new weapon, which was actually a further development of the existing one.
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