The 7.5×55mm Swiss or 7,5mm GP 11 (or unofficially 7.5×55mm Schmidt–Rubin) is a cartridge developed for the Swiss Army. It originated from the Gewehrpatrone 1890 (7.5×53.5mm) developed in 1898 by mechanical engineer Lt. Col. Eduard Rubin for rifles based on Rudolf Schmidt's action design. The 7.5×55mm Swiss GP 11 cartridge is similar in appearance to the slightly smaller 7.5×54mm French round though the two are not interchangeable.
History of preceding and related cartridge variants
Preceding GP 90 and GP 90/03 cartridges
The Gewehrpatrone 1890 cartridge has been in Swiss Army service since 1889 in their Schmidt–Rubin Model 1889 rifles. The previous generation of the military calibres used in Europe at the time were 10 to 14 mm (and black powder) as opposed to 7.5 mm of the Schmidt–Rubin ammunition, but the transition was underway in late 1880s (e. g., 8×50mmR Lebel was adopted in 1886 and 7.65×53mm Mauser in 1889). It was one of the first with 7.5 mm copper-jacketed rounds similar to those used today. Originally using PC 88 ("powder composition-88") ("low smoke" - equivalent to "smokeless") cut tubular smokeless single-base powder relying on nitrocellulose as its propellant ingredient, it was known as the Gewehrpatrone 1890. The Gewehrpatrone 1890 round 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 was far too corrosive, so it was updated in 1903 to the Gewehrpatrone 1890/03 cartridge.
GP 90/23 cartridge variant for the Model 1889 rifle
Long after the discontinuation of the Schmidt–Rubin Model 1889 rifle in the Swiss armed forces, the GP 90/03 cartridge was updated in 1923 and designated the Gewehrpatrone 1890/23 (officially abbreviated GP 90/23 after ca. 1961), for use in shooting competitions. The GP 90/23 was a 7.5×54.5mm round developed to be able to be used in arms chambered for Gewehrpatrone 1890 and GP 11 ammunition. The GP 90/23 operating chamber pressure was slightly higher compared to Gewehrpatrone 1890 ammunition and significantly lower compared to GP 11 ammunition. The GP 90/23 dispensed with the paper patching around the bullet and was loaded with a full metal jacket (FMJ) non-heeled round-nose bullet. The PC 88 propellant shape was changed to square flakes.
Gewehrpatrone 1890, Gewehrpatrone 1890/03 and GP 90/23 ammunition were 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 7.5mm Swiss round was updated to the completely non-corrosive 7.5×55mmm 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 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 rifles. 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.