7 . 5×55mm Swiss The 7 . 5×55mm Swiss or GP 11 ( or unofficially 7 . 5×55mm Schmidt Rubin ) is a cartridge developed for the Swiss Army by Lt . Col . Eduard Rubin for rifles based on Rudolf Schmidt ' s action design . The ammunition used by the Schmidt - Rubin Model 1889 rifle was one of the first to use 7 . 5 mm copper jacketed rounds similar to those used today . The GP90 7 . 5×53 . 5mm round designed by Colonel Rubin was revolutionary in that the most popular military calibres used in Europe at the time were around 12 . 7 mm as opposed to 7 . 5 mm of the Schmidt - Rubin ammunition . Oddly enough the round was " paper patched " meaning the actual bullet was wrapped around by a piece of paper , much like cotton patches were placed around the bullet of a musket . Paper patching the round was supposed to aid in the gas seal of the bullet . History of the cartridge variants . GP90 and GP90 / 03 cartridges . 7 . 5 mm Swiss cartridges have been in Swiss Army service since 1889 in their Schmidt - Rubin Model 1889 rifles . Originally using a semi - smokeless powder the cartridge was known as the Gewehrpatrone 1890 ( GP90 ) . It was discovered that the primer of GP90 ammunition was far too corrosive so it was updated in 1903 to the GP90 / 03 cartridge . While the scarcity of reloadable cartridge cases makes the 7 . 5 mm Swiss problematic for US shooters , large numbers of surplus rifles - especially the Model 1889 - have been imported . Reloadable cases can be easily produced by reforming . 284 Winchester brass . Case rims will be slightly undersized , but this presents no problems so long as the rifle ' s extractor is in good condition . This allows the handloader to produce a GP90 load that is safe for the Schmidt - Rubin Model 1889 rifle . GP90 / 23 the final cartridge variant for the Model 1889 rifle . Long after the discontinuation of the Schmidt - Rubin Model 1889 rifle in the Swiss Armed Forces the GP90 / 03 round was updated in 1923 and called the GP90 / 23 , for use in shooting competitions . The GP90 / 23 discarded the paper patching around the bullet and the semi - smokeless powder was replaced by smokeless powder propellant . The GP 11 cartridge . In 1911 the metallurgy and bolt design in Swiss military rifles had advanced enough that a more powerful cartridge could be used in the Model 1911 rifles and Schmidt - Rubin 1896 / 11 rifles . The 7 . 5 mm Swiss round was updated to the completely non - corrosive Gewehrpatrone 1911 ( GP 11 ) . Besides being used in the Model 1911 rifles and Schmidt - Rubin 1896 / 11 rifles , GP 11 ammunition was also used in the MG 11 machine gun , K11 and K31 carbines as well as in the Stgw 57 battle rifle . The cartridge saw extensive service until the early 1990s with the standard rifles of Swiss servicemen , and still sees use by Swiss Army reservists , and sport shooters , of which there are many . Furthermore , it is still the standard ammunition for the MG 51 general purpose machine gun used on many Swiss armored vehicles such as the Pz 87 " Leopard 2 " tank or the MOWAG Eagle Reconnaissance Vehicle . In this role , it is usually belt fed with GP 11 full metal jacket and GP 11 tracer rounds . The 11 . 3 gram ( 174 grain ) Full Metal Jacket GP 11 spitzer bullet offered good aerodynamic efficiency and ballistic performance with a ballistic coefficient ( G1 BC ) of 0 . 505 to 0 . 514 ( ballistic coefficients are somewhat debatable ) . At 780 m / s ( 2560 ft / s ) muzzle velocity the standard GP 11 ball bullet retained supersonic velocity up to 800 m ( 875 yards ) ( V ≈ Mach 1 . 1 ) under ICAO Standard Atmosphere conditions at sea level ( air density ρ = 1 . 225 kg / m ) . Even by contemporary ( 2007 ) standards 800 m ( 875 yards ) typical effective range is quite remarkable for a standard military rifle round . GP 11 is regarded as highly accurate and well - manufactured ammunition . Due to the increased availability of K31 rifles on the civilian market , a number of cartridge manufacturers , including Prvi Partizan and Hornady , now produce 7 . 5×55mm rounds in full metal jacket , soft - tip , and ballistic tip configurations . In addition to the standard Full Metal Jacket GP 11 rounds , specialty rounds were produced as well . Armor - piercing steel - cored rounds can be identified by their violet bases . These rounds can easily pierce 5 mm ( 0 . 2 in ) of steel plate at 500 m ( 550 yards ) . Tracer rounds burn out to 800 m ( 875 yards ) , and can be identified by their red tips . Despite its nomenclature , the 7 . 5×55mm Swiss can with proper care use the same 7 . 62 mm ( . 308 in ) bullets as conventional Western 7 . 62 mm ( . 308 in ) cartridges that have slightly wider land and groove diameters . This allows for ease of handloading and custom competition or hunting loads , as nearly any . 308 diameter bullet may be used . However , most Swiss match shooters use standard GP 11 ammunition , a testament to the accuracy of the GP 11 round . Specifications . Variants overview . Due to the greater pressure produced by the GP 11 round , it is not safe to fire GP 11 rounds in Model 1889 Schmidt - Rubin rifles . 7 . 5×55mm Swiss / GP 11 . The 7 . 5×55mm Swiss cartridge has 4 . 22 ml ( 65 grains ) HO cartridge case capacity . The exterior shape of the case was designed to promote reliable case feeding and extraction in bolt action rifles and machine guns alike , under extreme conditions . 7 . 5×55mm Swiss maximum C . I . P . cartridge dimensions . All sizes in millimeters ( mm ) . Americans would define the shoulder angle at alpha / 2 ≈ 30 . 5 degrees . The common rifling twist rate for this cartridge is 270 mm ( 1 in 10 . 63 in ) , 4 grooves , Ø lands = 7 . 51 mm , Ø grooves = 7 . 77 mm , land width = 3 . 75 mm and the primer type is large rifle . According to the official C . I . P . ( Commission Internationale Permanente pour l ' Epreuve des Armes à Feu Portatives ) guidelines the 7 . 5×55mm Swiss case can handle up to 380 MPa ( 55 , 114 psi ) piezo pressure . In C . I . P . regulated countries every rifle cartridge combo has to be proofed at 125 % of this maximum C . I . P . pressure to certify for sale to consumers . Switzerland is not a C . I . P . member state and therefore does not recognize any C . I . P . rulings and proofed its military 7 . 5×55mm rifles chambered in the GP 11 version of their service cartridge at 150 % of the GP 11 load pressure of 313 . 717 MPa ( 45 , 500 psi ) . This means a Swiss military proof test would be executed at 1 . 5 * 313 . 717 = 470 . 57 MPa ( 68 , 250 psi ) and a C . I . P . proof test would be executed at ( 68 , 892 psi ) . Swiss 7 . 5×55mm GP 11 proof tests are therefore not recognized in C . I . P . member states in their turn .