7.5×55mm Swiss

Swiss rifle cartridge
the rifle cartridge

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.

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") rauchschwacher ("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.

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.

Gewehrpatrone 1890 Gewehrpatrone 1890/03 GP 90/23 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) 0.3028 in(0.3075 in) 0.3028 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 grsmokeless 31 grsmokeless 33.7 grsmokeless 49.35 grsmokeless Max. service load chamber pressure(Swiss standards) 36,970 psi 36,970 psi 38,390 psi 45,500 psi

Due to the greater pressures produced by the GP 11 rounds, they are not safe to be fired in Model 1889 Schmidt–Rubin rifles which have bore diameters of 0.305 0.306".

The 7.5×55mm Swiss / GP 11 cartridge (designated as the 7.5 × 55 Suisse by the C. I. P.)

Due to the availability of surplus K31 rifles on the civilian market, a number of cartridge manufacturers, such as Prvi Partizan, 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.

Despite its nomenclature, the 7.5×55mm Swiss designed for 7.78 mm (0.306 in) bullets can use the same 7.62 mm (.308 in) bullets as conventional 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 military 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 newly made brass for reloaders as well as loaded ammunition so supplies of reloadable brass are less difficult to obtain.