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7.5×55mm Swiss

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7.5x55mm GP11
Two 7x57 cartridges (left) next to a 7.5x55mm / GP11 (mid), .308 Win (right) and .223 Rem (far right)
TypeRifle
Place of origin  Switzerland
Service history
In service1889-present
Used bySwitzerland
WarsWorld War II, First Indochina War, Algerian War, Suez Crisis, Vietnam War
Production history
DesignerEduard Rubin
Designed1889
Produced1889-present
VariantsGP90, GP90/03, GP90/23, GP11
Specifications
Case typeRimless, bottleneck
Bullet diameter7.77 mm (0.306 in)
Neck diameter8.50 mm (0.335 in)
Shoulder diameter11.60 mm (0.457 in)
Base diameter12.60 mm (0.496 in)
Rim diameter12.65 mm (0.498 in)
Rim thickness1.65 mm (0.065 in)
Case length55.60 mm (2.189 in)
Overall length77.70 mm (3.059 in)
Case capacity4.22 cm3 (65.1 gr H2O)
Rifling twist270 mm (1 in 10.63 in)
Primer typeLarge rifle
Maximum pressure380 MPa (55,000 psi)
Ballistic performance
Bullet mass/type Velocity Energy
130 gr (8 g) SP 3,000 ft/s (910 m/s) 2,608 ft⋅lbf (3,536 J)
150 gr (10 g) SP 2,820 ft/s (860 m/s) 2,658 ft⋅lbf (3,604 J)
180 gr (12 g) SP 2,570 ft/s (780 m/s) 2,642 ft⋅lbf (3,582 J)
200 gr (13 g) SP 2,460 ft/s (750 m/s) 2,700 ft⋅lbf (3,700 J)
Source(s): Cartridges of the World[1]

The 7.5x55mm Swiss or GP11 (or unofficially 7.5x55mm Schmidt Rubin) is a cartridge developed for the Swiss Army by 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 7.5x53.5mm 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.

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 GP11 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 (GP11). Besides being used in the Model 1911 rifles and Schmidt-Rubin 1896/11 rifles, GP11 ammunition was also used in the K11 and K31 carbines as well as in the Stgw 57 battle rifle. The cartridge saw extensive service until the early 1990s and is now phased out, but nevertheless still sees use by Swiss Army reservists, and sport shooters, of which there are many.

The 11.3 gram (174 grain) Full Metal Jacket GP11 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 GP11 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[2].

GP11 is regarded as highly accurate and well-manufactured ammunition. Due to the increased availability of former Swiss K-31 rifles on the civilian market, a number of cartridge manufacturers, including Prvi Partizan and Hornady, now produce 7.5x55mm rounds in FMJ, soft-tip, and ballistic tip configurations.

In addition to the standard Full Metal Jacket GP11 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 bases.

Despite its nomenclature, the 7.5x55mm 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 GP11 ammunition, a testament to the accuracy of the GP11 round.

Specifications

Variants overview

Stripper clip with 7.5x55mm Swiss GP11 cartridges.
GP90 GP90/03 GP90/23 GP11
Cartridge 7.5x53.5mm 7.5x53.5mm 7.5x54.5mm 7.5x55mm
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 GP11 round, it is not safe to fire GP11 rounds in Model 1889 Schmidt-Rubin rifles!

7.5x55mm Swiss / GP11

The 7.5x55mm Swiss cartridge has 4.22 ml (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.

7.5x55mm 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 7.5x55mm Swiss case can handle up to 380 MPa (55114 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 7.5x55mm rifles chambered in the GP11 version of their service cartridge at 150% of the GP11 load pressure of 313.717 MPa (45500 psi). This means a Swiss military proof test would be executed at 1.5 * 313.717 = 470.57 MPa (68250 psi) and a C.I.P. proof test would be executed at 1.25 * 380 = 475 MPa (68892 psi). Swiss 7.5x55mm GP11 proof tests are therefore not recognized in C.I.P. member states in their turn.

See also

References

  1. ^ Barnes, Frank C. (2006) [1965]. Skinner, Stan (ed.). Cartridges of the World (11th Edition ed.). Iola, WI, USA: Gun Digest Books. pp. 353, 375. ISBN 0-89689-297-2. {{cite book}}: |edition= has extra text (help)
  2. ^ Maximum effective rifle range
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