7.5×55mm Swiss

7.5×55mm GP 11

Two 7×57 cartridges (left) next to a 7.5×55mm / GP 11 (mid), .308 Win (right) and .223 Rem (far right)
Type Rifle
Place of origin   Switzerland
Service history
In service 1889–present
Used by Switzerland
Wars World War II (Armed neutrality)
Production history
Designer Eduard Rubin
Designed 1889
Produced 1889–present
Variants GP90, GP90/03, GP90/23, GP 11
Specifications
Case type Rimless, bottleneck
Bullet diameter 7.77 mm (0.306 in)
Neck diameter 8.50 mm (0.335 in)
Shoulder diameter 11.60 mm (0.457 in)
Base diameter 12.60 mm (0.496 in)
Rim diameter 12.65 mm (0.498 in)
Rim thickness 1.65 mm (0.065 in)
Case length 55.60 mm (2.189 in)
Overall length 77.70 mm (3.059 in)
Case capacity 4.22 cm3 (65.1 gr H2O)
Rifling twist 270 mm (1 in 10.63 in)
Primer type Berdan or Boxer Large rifle
Maximum pressure 380 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)
174 gr (11 g) GP 11 2,560 ft/s (780 m/s) 2,535 ft·lbf (3,437 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]

For the 7.5mm Swiss pistol round, see 7.5mm 1882 Ordnance

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 10 to 14 mm as opposed to 7.5 mm of the Schmidt–Rubin ammunition.

History of the cartridge variants

GP90 and GP90/03 cartridges

GP90/03 ammunition

7.5 mm Swiss cartridges have been in Swiss Army service since 1889 in their Schmidt–Rubin Model 1889 rifles. Originally using PC 88 ("powder composition-88") rauchschwacher (literally "low smoke") cut tubular smokeless single-base powder relying on nitrocellulose as its propellant ingredient it was known as the Gewehrpatrone 1890 (GP90). 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 2 turns of paper, much like cotton patches were placed around the bullet of a musket. This paper patching was supposed to aid in the gas seal of the bullet and reduce metallic fouling of the barrel.

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

PC 88 square flake shaped propellant used in the GP 90/23 cartridge variant

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 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 9 different variants, all models combined.[2]

The GP 11 cartridge

Swiss Army issue 10-round GP 11 pack.

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). 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 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 GP 11 cartridge used double-base powder combining nitrocellulose (gun cotton) with about 30% nitroglycerin as propellants. The 11.3 gram (174 grain) Full Metal Jacket GP 11 spitzer bullet contained a lead/antimony core. The 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 bullet featured a boat tail and 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 (2,559 ft/s) muzzle velocity the standard GP 11 ball bullet retained supersonic velocity up to 800 m (874.9 yd) (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 yd) typical effective range is quite remarkable for a standard military rifle round.[3] The GP 11 cartridge cases were made of brass (72% of copper and 28% zinc) or from May 1943 to January 1947 due to supply shortages in Switzerland of aluminum or steel.

Maximum range with the GP 11 under Swiss chosen atmospheric conditions (altitude = 800 m (2,625 ft), air pressure = 649 mm (25.55 in) Hg, temperature = 7 °C (45 °F)) equaling ICAO Standard Atmosphere conditions at 653.2 m (2,143 ft) (air density ρ = 1.150 kg/m3) is acquired when the barrel is elevated 37° and is muzzle velocity dependent.[4]

Muzzle velocity Maximum range
760 m/s (2,493 ft/s) 5,000 m (5,468 yd)
780 m/s (2,559 ft/s) 5,500 m (6,015 yd)
810 m/s (2,657 ft/s) 5,800 m (6,343 yd)

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 30 kgf (66 lbf) (1911), 50 kgf (110 lbf) (1929 modification), 100 kgf (220 lbf) (1942 modification) 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 Rotenburg and Solothurn as other municipalities in Switzerland.

GP 11 is regarded as highly accurate and well-manufactured 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-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.[5]

GP 11 ammunition was available in 40 different versions, all models combined.[6]

Specifications

Variants overview

Stripper clip with 7.5×55mm Swiss GP 11 cartridges.
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
smokeless 		31 gr
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 / GP 11 cartridge (designated as the 7.5 × 55 Suisse by the C.I.P.)[7] 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.

7.5×55mm Swiss / GP 11 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 (0.296 in), Ø grooves = 7.77 mm (0.306 in), land width = 3.75 mm (0.148 in), and the primer type is Berdan or large rifle.

According to the official C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) rulings the 7.5×55mm Swiss can handle up to 380.00 MPa (55,114 psi) 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.[7] This means that 7.5×55mm Swiss / GP 11 chambered arms in C.I.P. regulated countries are currently (2016) proof tested at 475.00 MPa (68,893 psi) 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 (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 1.25 * 380 = 475 MPa (68,892 psi). 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 12.72 mm (0.501 in) diameter bolt face the 7.5×55mm Swiss GP 11 was and is rarely chambered in civilian target or hunting guns made outside Switzerland.[7]

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 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 surplus ammunition, a testament to the accuracy 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 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. Privi 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

See also

References

  1. ↑ Barnes, Frank C. (2006) [1965]. Skinner, Stan, ed. Cartridges of the World (11th ed.). Iola, WI, USA: Gun Digest Books. pp. 353, 375. ISBN 0-89689-297-2.
  2. ↑ Die Repetiergewehre der Schweiz p. 197
  3. ↑ Maximum effective rifle range
  4. ↑ Règl. No. 65.1f p. 65
  5. ↑ Swiss Army Sturmgewehr 57 Manual (German)
  6. ↑ Die Repetiergewehre der Schweiz p. 197 to 199
  7. 1 2 3 C.I.P. TDCC datasheet 7,5 x 55 Suisse
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