7.5×55mm Swiss


The 7.5×55mm Swiss or GP 11 is a cartridge developed for the Swiss Army by mechanical engineer 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 Rubin was revolutionary in that the most popular military calibres used in Europe at the time were around 10 to 14 mm as opposed to 7.5 mm of the Schmidt–Rubin ammunition. The 7.5x55mm Swiss cartridge is similar in appearance to the slightly smaller 7.5x54mm French round though the two are not interchangeable.

History of the cartridge variants

GP90 and GP90/03 cartridges

The 7.5 mm Swiss cartridge has been in Swiss Army service since 1889 in their Schmidt–Rubin Model 1889 rifles. Originally using PC 88 rauchschwacher cut tubular smokeless single-base powder relying on nitrocellulose as its propellant ingredient, it was known as the Gewehrpatrone 1890. The GP90 was loaded with a paper patched lead hollow based heeled steel-capped round-nose bullet. Starting from the rear of the nose section the bullets were wrapped around by two turns of paper, much like cotton patches were placed around the bullet of a musket. This paper patching reduced metallic fouling of the barrel and was supposed to aid in the gas seal of the bullet.
It was discovered that the primer of GP90 ammunition was far too corrosive so it was updated in 1903 to the GP90/03 cartridge.

GP90/23 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 dispensed with the paper patching around the bullet and was loaded with a full metal jacket non-heeled round-nose bullet. The PC 88 propellant shape was changed to square flakes.
GP90, GP90/03 and GP90/23 ammunition was available in nine different variants.

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. The bolt thrust of the GP 11 round is relatively high compared to many other service rounds used in the early 20th century. 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 and 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 GP 11 cartridge used double-base powder combining nitrocellulose with about 30% nitroglycerin as propellants.
The full metal jacket GP 11 boat tail spitzer bullet was when adopted an innovative bullet design. The GP 11 bullet contained a lead-antimony core and its jacket was made of plated steel or tombac. Depending on the year of production the plating was made of copper, brass, nickel or copper-nickel. The GP 11 cartridge cases were made of brass or, from May 1943 to January 1947, due to supply shortages in Switzerland, of aluminum or steel. The GP 11 bullet offered good aerodynamic efficiency and ballistic performance with a ballistic coefficient of 0.505 to 0.514. At muzzle velocity the standard GP 11 ball bullet retained supersonic velocity up to under ICAO Standard Atmosphere conditions at sea level. Even by 2011 standards, typical effective range is quite remarkable for a standard military rifle round that is more than a century old.
Maximum range with the GP 11 under Swiss chosen atmospheric conditions equaling ICAO Standard Atmosphere conditions at is acquired when the barrel is elevated 37° and is muzzle velocity dependent.
Muzzle velocityMaximum range

The GP 11 bullet set off the militaries of countries like Germany, the United States and the United Kingdom at the onset of and after World War I to develop and field similar full metal jacket boat tail spitzer bullets to improve the maximum range and long range performance of the full metal jacket flat based spitzer bullet designs they used.
Since its introduction in 1911 the GP 11 cartridge featured some technical development. The projectile-seating in the cartridge case neck was improved by adding a cannelure on the bullet and crimping the case neck over time, resulting in , , extraction force. In 1942 the square flake-shaped double-base propellant was replaced by tubular shaped double-base propellant. Further, there were minor developments regarding the projectiles, sealing and primers. GP 11 cartridges were mass-produced for the Swiss military in the ammunition factories in Altdorf and in Thun until 1994. The last 1994 produced ammunition had lot No. 349-94. Previously GP 11 was also produced in Rotenburg and Solothurn as other municipalities in Switzerland.
GP 11 is regarded as highly accurate and well-manufactured service ammunition. For Swiss military service ammunition the primer-type is Berdan. Berdan-primed ammunition is not easy for reloading previously fired cartridges.
In addition to the standard full metal jacket GP 11 rounds, specialty rounds were produced as well for the Swiss military. Armor-piercing steel-core rounds can be identified by their violet bases. These rounds can easily pierce 5 mm of steel plate at 500 m. Tracer rounds burn out to 800 m, and can be identified by their red tips.
When all modifications are combined GP 11 ammunition was available in a total of 40 different versions.

Specifications

Variants overview

GP90GP90/03GP90/23GP 11
Cartridge7.5×53.5mm7.5×53.5mm7.5×54.5mm7.5×55mm
Case length2.106 in2.106 in2.15 in2.185 in
Rim diameter0.492 in0.492 in0.5 in0.496 in
Head diameter0.488 in0.488 in0.496 in0.493 in
Neck diameter
0.362 in
0.362 in
0.328 in0.334 in
Bullet211 gr211 gr190 gr174 gr
Bullet diameter
0.3208 in
0.3208 in
0.3075 in0.306 in
Bullet length1.14 in1.14 in1.165 in1.378 in
Muzzle velocity1968 ft/s1980 ft/s2050 ft/s2560 ft/s
Powder measure27-31 gr
smokeless		31 gr
smokeless		33.7 gr
smokeless		49.35 gr
smokeless
Max. service load chamber pressure
36,970 psi36,970 psi38,390 psi45,500 psi

Due to the greater pressures produced by the GP 11 rounds, they are not fired in Model 1889 Schmidt–Rubin rifles.

7.5×55mm Swiss / GP 11

The 7.5×55mm Swiss / GP 11 cartridge has 4.22 ml 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 / GP 11 maximum C.I.P. cartridge dimensions. All sizes in millimeters.
Americans would define the shoulder angle at alpha/2 ≈ 30.5 degrees. The common rifling twist rate for this cartridge is 270 mm, 4 grooves, Ø lands =, Ø grooves =, land width =, and the primer type is Berdan or large rifle.
According to the official Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives rulings, the 7.5×55mm Swiss can handle up to Pmax 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. This means that 7.5×55mm Swiss / GP 11 chambered arms in C.I.P. regulated countries are currently proof tested at PE piezo pressure.
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. This means a Swiss military proof test would be executed at 1.5 * 313.717 = 470.57 MPa and a C.I.P. proof test would be executed at . Swiss 7.5×55mm GP 11 proof tests are therefore not recognized in C.I.P. member states in their turn.

Civilian use

Due to the uncommon diameter bolt face the 7.5×55mm Swiss GP 11 was and is rarely chambered in civilian target or hunting guns made outside Switzerland.
Due to the increased availability of surplus K31 rifles on the civilian market, a number of cartridge manufacturers, including Prvi Partizan and Hornady, now produce 7.5×55mm GP 11-like rounds in full metal jacket, soft-tip, and ballistic tip configurations. Civilian manufacturers also produce similar cartridge cases with Boxer large rifle primers for easier reloading.

Reloading

Despite its nomenclature, the 7.5×55mm Swiss can use the same 7.62 mm bullets as conventional 7.62 mm 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 surplus ammunition, a testament to the quality of the factory loading
of the GP 11 round.
While the scarcity of reloadable cartridge cases previously made the 7.5 mm Swiss problematic for US shooters, reloadable cases are easily produced by reforming.284 Winchester brass. Case rims are 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. Prvi Partizan has been producing new made brass for reloaders as well as loaded ammunition so supplies of reloadable brass are less difficult to obtain.

Use