7.5 x 55 Schmidt Rubin
Encyclopedia
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.
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 problematical 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.
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 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) (V800 ≈ Mach
1.1) under ICAO Standard Atmosphere conditions at sea level (air density ρ = 1.225 kg/m3). 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 7.82 mm (.308 in) bullets as conventional Western 7.62 mm (.30 calibre) 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 lead core bullet may be used. However, most Swiss match shooters use standard GP 11 ammunition, a testament to the accuracy of the GP 11 round.
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!
(65 grains
) H2O 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.
Cartridge (firearms)
A cartridge, also called a round, packages the bullet, gunpowder and primer into a single metallic case precisely made to fit the firing chamber of a firearm. The primer is a small charge of impact-sensitive chemical that may be located at the center of the case head or at its rim . Electrically...
developed for the Swiss Army by Lt. Col. Eduard Rubin
Eduard Rubin
Lieutenant Colonel Eduard Rubin was a Swiss firearm designer who is most notable for inventing the full metal jacket bullet in 1882. His most famous cartridge was the 7.5x55mm Swiss. He served as director of the Swiss Federal Ammunition Factory and Research Center in Thun.-References:...
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.
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 ammunitionAmmunition
Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...
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 problematical 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
.284 Winchester
The .284 Winchester is an example of a commercially rather unsuccessful cartridge that has enjoyed a resurgence in interest due to interest from long-range competitive shooters...
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. 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
Schmidt-Rubin
The Schmidt-Rubin rifles were a series of Swiss Army service rifles in use between 1889 and 1953. They are distinguished by the straight-pull bolt action invented by Rudolf Schmidt and use Eduard Rubin's 7.5x55mm rifle cartridge.-Schmidt-Rubin 1889:...
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
MG 11
The Maschinengewehr Modell 1911 or MG 11 is a Swiss heavy machine gun which was introduced before and during the First World War. The MG 11 has a narrow constructive relationship with the German MG 08 heavy machine gun.-History:...
machine gun, K11 and K31
K31
The Karabiner Model 1931 is a magazine-fed, straight-pull bolt-action rifle. It was the standard issue rifle of the Swiss armed forces from 1933 until 1958, though examples remained in service into the 1970s...
carbines as well as in the Stgw 57 battle rifle
Battle rifle
A battle rifle is a military service rifle that fires a full power rifle cartridge, such as 7.62x51mm NATO. While the designation of battle rifle is usually given to post-World War II select fire infantry rifles such as the H&K G3, the FN FAL or the M14, this term can also apply to older military...
. 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
General purpose machine gun
A general-purpose machine gun is a multi-purpose weapon: it is a machine gun firing a full-power rifle cartridge and which can be used in a variety of roles, from a bipod- or tripod-mounted infantry support weapon to a helicopter door gun or a vehicle-mounted support weapon...
used on many Swiss armored vehicles such as the Pz 87 "Leopard 2"
Leopard 2
The Leopard 2 is a main battle tank developed by Krauss-Maffei in the early 1970s for the West German Army. The tank first entered service in 1979 and succeeded the earlier Leopard 1 as the main battle tank of the German Army. Various versions have served in the armed forces of Germany and twelve...
tank or the MOWAG Eagle
MOWAG Eagle
The MOWAG Eagle is a wheeled armored vehicle designed by the Swiss MOWAG corporation. It has gone through several generations of development. The current vehicle, introduced in November 2003, is the Eagle IV, which is based on the Duro IIIP chassis...
Reconnaissance Vehicle. In this role, it is usually belt fed
Belt (firearm)
A belt or ammunition belt is a device used to retain and feed cartridges into a firearm. Belts and the associated feed systems are typically employed to feed machine guns or other automatic weapons...
with GP 11 full metal jacket
Full metal jacket bullet
A full metal jacket is a bullet consisting of a soft core encased in a shell of harder metal, such as gilding metal, cupronickel or less commonly a steel alloy. This shell can extend around all of the bullet, or often just the front and sides with the rear left as exposed lead...
and GP 11 tracer
Tracer ammunition
Tracer ammunition are bullets that are built with a small pyrotechnic charge in their base. Ignited by the burning powder, the phosphorus tail burns very brightly, making the projectile visible to the naked eye...
rounds.
The 11.3 gram (174 grain) Full Metal Jacket GP 11 bullet offered good aerodynamic efficiency and ballistic performance with a ballistic coefficient
Ballistic coefficient
In ballistics, the ballistic coefficient of a body is a measure of its ability to overcome air resistance in flight. It is inversely proportional to the negative acceleration—a high number indicates a low negative acceleration. BC is a function of mass, diameter, and drag 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
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
velocity up to 800 m (875 yards) (V800 ≈ Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
1.1) under ICAO Standard Atmosphere conditions at sea level (air density ρ = 1.225 kg/m3). 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
Prvi Partizan
Prvi Partizan is an ammunition manufacturer, located in Užice, Serbia. Founded in 1928 as FOMU - Fabrika Oružje Municija Užice. The company produces ammunition for civilian and military consumers in a variety of calibers in various loadings. Their products are available worldwide...
and Hornady
Hornady
Hornady Manufacturing Company is an American manufacturer of ammunition and handloading components, based in Grand Island, Nebraska.The company was founded by Joyce Hornady in 1949 and is currently run by his son Steve Hornady who took over after his father's death in a plane crash in 1981.Hornady...
, now produce 7.5×55mm rounds in full metal jacket
Full metal jacket bullet
A full metal jacket is a bullet consisting of a soft core encased in a shell of harder metal, such as gilding metal, cupronickel or less commonly a steel alloy. This shell can extend around all of the bullet, or often just the front and sides with the rear left as exposed lead...
, soft-tip
Soft point bullet
A soft-point bullet , also known as a soft-nosed bullet, is a lead expanding bullet with a copper or brass jacket that is left open at the tip, exposing some of the lead inside and is thus an example of a semi-jacketed round...
, 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
Tracer ammunition
Tracer ammunition are bullets that are built with a small pyrotechnic charge in their base. Ignited by the burning powder, the phosphorus tail burns very brightly, making the projectile visible to the naked eye...
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 7.82 mm (.308 in) bullets as conventional Western 7.62 mm (.30 calibre) cartridges that have slightly wider land and groove diameters. This allows for ease of handloading
Handloading
Handloading or reloading is the process of loading firearm cartridges or shotgun shells by assembling the individual components , rather than purchasing completely assembled, factory-loaded cartridges...
and custom competition or hunting loads, as nearly any .308 diameter lead core bullet may be used. However, most Swiss match shooters use standard GP 11 ammunition, a testament to the accuracy of the GP 11 round.
Variants overview
| GP90 | GP90/03 | GP90/23 | GP 11 | |
| Cartridge | 7.5×53.5mm | 7.5×53.5mm | 7.5×54.5mm | 7.5×55mm |
| Case length | 2.106 in | 2.106 in | 2.15 in | 2.185 in |
| Rim diameter | 0.492 in | 0.492 in | 0.5 in | 0.496 in |
| Head diameter | 0.488 in | 0.488 in | 0.496 in | 0.493 in |
| Neck diameter (w/ paper patch) |
0.362 in (0.362 in) |
0.362 in (0.335 in) |
0.328 in | 0.334 in |
| Bullet | 211 gr | 211 gr | 190 gr | 174 gr |
| Bullet diameter (w/ paper patch) |
0.3208 in (0.3075 in) |
0.3208 in (0.3086 in) |
0.3075 in | 0.306 in |
| Bullet length | 1.14 in | 1.14 in | 1.165 in | 1.378 in |
| Muzzle velocity | 1968 ft/s | 1980 ft/s | 2050 ft/s | 2560 ft/s |
| Powder measure | 27-31 gr semi-smokeless |
31 gr semi-smokeless |
33.7 gr smokeless |
49.35 gr smokeless |
| Max. service load chamber pressure (Swiss standards) |
36,970 psi | 36,970 psi | 38,390 psi | 45,500 psi |
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 mlLitre
pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...
(65 grains
Grain (measure)
A grain is a unit of measurement of mass that is nominally based upon the mass of a single seed of a cereal. From the Bronze Age into the Renaissance the average masses of wheat and barley grains were part of the legal definition of units of mass. However, there is no evidence of any country ever...
) H2O 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
Rifling
Rifling is the process of making helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis...
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
Percussion cap
The percussion cap, introduced around 1830, was the crucial invention that enabled muzzleloading firearms to fire reliably in any weather.Before this development, firearms used flintlock ignition systems which produced flint-on-steel sparks to ignite a pan of priming powder and thereby fire the...
is large rifle.
According to the official C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives
Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives
The Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives is an international organisation whose members are 14 states, mainly European....
) 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.
See also
- List of rifle cartridges
- 7 mm caliber7 mm caliberThis article lists firearm cartridges which have a bullet in the to caliber range.*Length refers to the cartridge case length.*OAL refers to the overall length of the cartridge....
- Schmidt-RubinSchmidt-RubinThe Schmidt-Rubin rifles were a series of Swiss Army service rifles in use between 1889 and 1953. They are distinguished by the straight-pull bolt action invented by Rudolf Schmidt and use Eduard Rubin's 7.5x55mm rifle cartridge.-Schmidt-Rubin 1889:...
- K31K31The Karabiner Model 1931 is a magazine-fed, straight-pull bolt-action rifle. It was the standard issue rifle of the Swiss armed forces from 1933 until 1958, though examples remained in service into the 1970s...
- SIG 510SIG 510The SIG SG 510 or Sturmgewehr 57 is an automatic rifle manufactured by Schweizerische Industrie Gesellschaft of Switzerland. It uses a similar roller-delayed blowback system to the H&K G3 and CETME rifles...
External links
- The History The 7.5 Swiss Cartridge
- 7,5×55 Swiss information from Norma
- 7.5 × 55 Swiss at www.reloadersnest.com
- Gian-Marchet 7,5 × 55 Schweizer Patronen Page (including images)