Stg.45(M) - German predecessor to CETME rifles, made at the Mauser Werke in 1945

Early CETME assault rifle prototype chambered for experimental 7.92x40mm cartridge

CETME modelo A assault rifle, chambered for 7.62x51mm reduced load cartridge

CETME modelo B / mod. 58 with 30 rounds magazine

CETME modelo C rifle (semi-automatic only "Sporter" version shown)

data for CETME mod. B / Mod. 58 rifle
Caliber: 7.62x51 mm reduced power load; also 7.62x51mm NATO
Action: delayed blowback
Overall length: 1015 mm
Barrel length: 450 mm
Weight: 4.4 kg
Rate of fire: 550 - 600 rounds per minute
Magazine capacity: 20 or 30 rounds

The Spanish state company CETME (Centro de Estudios Tecnicos de Materiales Especiales - Special Materials Technical Studies Center, now known as Empresa National Santa Barbara) was founded in 1949 to develop various small arms for Spanish army. At about the same time it employed the German arms designer Ludwig Vorgrimler, who worked for the famous Mauser Werke in Germany before and during the World War 2. The Vorgrimler was the designer of the experimental German assault rifle, known as "Gerat 06" or Stg.45(M). This rifle was not manufactured in any quantities, but its design served as a basis for further development at the CETME, and more important, at the another German company, Heckler & Koch, which obtained a license for the Vorgrimler / CETME rifle design circa 1957. This deal later resulted in the famous family of the H&K weapons, like the G3 and HK33 assault rifles, HK21 and HK23 machine guns, MP5 submachine guns and numerous other small arms that achieved a worldwide popularity. All those weapons are built using the delayed blowback system of operation, designed by Vorgrimler and his men at the Mauser in 1945 and refined by CETME.
The initial assault rifle development at the CETME was conducted around proprietary intermediate cartridge, known as 7.92x40mm CETME. This cartridge featured a long and streamlined bullet, made from aluminum. The overall design was found adequate, but cartridge was rejected in favor of the 7.62x51mm round with lighter bullet and a reduced powder charge. Improved rifle entered serial production in 1956 and was adopted by the Spanish army in 1957. In 1958 CETME introduced a slightly improved design, known as Modelo B or Model 58. This rifle was intended to fire 7.62x51mm reduced loads but also could fire the standard 7.62mm NATO, if the bolt group and the return spring are replaced with the appropriate set of parts. In 1964, CETME introduced the Modelo C, which also was adopted by Spanish Army, Navy and Air Force. This rifle was intended to fire only standard, full power 7.62x51mm NATO ammunition. Its key improvements were 4-position diopter sights (instead of the earlier leaf type open sights), wooden handguards instead of earlier steel ones, bipod was made as a separate part and, most important, the chamber was fluted to improve extraction and avoid torn rims and cartridge case failures in harsh environment conditions. Production of the modelo C rifle was ceased in 1976, and in 1980s it had been gradually replaced by its 5.56mm derivative, CETME Modelo L assault rifle.
All 7.62mm CETME rifles are built around Vorgrimlers' roller delayed blowback system. This system employs a two parts bolt with two rollers. The front bolt part (bolt head) is relatively light and has a bolt face with extractor on it. It also has a hollow cavity at the rear, in which an inclined forward end of the rear part of the bolt (bolt body) is inserted. The system features two rollers, inserted from the sides into the bolt head and rested on the inclined forward end of the bolt body (see this diagram; it will pop up in the new window). When gun is fired, the pressure began to move the cartridge back against the bolt face. The rollers, which are extended into the recesses in the barrel extension, began to move inward into the bolt head, due to inclined shape of the recesses. This movement translates into the faster rearward movement of the heavier bolt body, so, at the initial moments of shot, when pressure in the chamber is still high, bolt face moves relatively slow. When pressure drops to a reasonable level, rollers disengage the barrel extension completely and from this moment on the bolt head and the bolt body move backward at the same speed, extracting and ejecting spent case and chambering a fresh cartridge on the way back. All CETME rifles are firing from the closed bolt. The trigger mechanism is hammer fired, and in military versions is capable in semi-automatic and fully automatic modes of fire. On the early models the safety / fire mode selector switch was located above the trigger at the right side of the gun. From the model C the safety / selector switch was relocated to the left side of the gun. The receiver is made from steel sheet stampings, as well as the trigger group housing, which is hinged to the receiver just behind the magazine housing. Early models (prior to Modelo C) were issued with integral folding metallic bipods and open leaf-type rear sights. The Modelo C rifles were issued with wooden handguards and a separate detachable bipods. The rear sights were replaced by the 4 positions diopter sights, marked for 100 - 400 meters range. All rifles featured a wooden buttstock and a folding carrying handle above the receiver. The flash hider of the Modelo C rifles was shaped to accept and launch NATO-standard rifle grenades. Most rifles were issued with magazines of 20 rounds capacity and made of steel, but 30 rounds magazines also were available.