7.5 x 55 Schmidt Rubin

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The 7.5x55 Schmidt Rubin (or 7.5 mm Swiss) is a cartridge developed for the Swiss Army by Eduard Rubin for rifles based on Rudolf Schmidt's action design.

NOTE GP11 ammunition should never be fired in older Schmidt-Rubin rifles such as the 1889 rifle. Use only GP90 ammunition in these.

[edit] General information

The 7.5x55 cartridge has been in Swiss Army service since 1889. Originally using a semi-smokeless powder it was known as the Gewehrpatrone 1890 (GP90). It was discovered that the primer of GP90 ammunition was far too corrosive so it was updated to the GP 1890/03 cartridge. This cartridge was updated still using smokeless powder and called the GP 1890/23.

In 1913 the metallurgy in Schmidt-Rubin rifles had advanced enough that a more powerful cartridge could be used. The 7.5 Swiss round was updated to the Gewehrpatrone 1911 (GP11). GP11 ammunition was used in the K11 and K31 carbines as well as the Stg.57 assault rifle. The cartridge saw service until the mid-80s. GP11 is regarded as highly accurate and well manufactured ammunition.

Despite it's nomenclature, the 7.5x55mm Swiss uses the same .308" bullets as conventional Western 7.62mm (.30 caliber) cartridges.

[edit] Specifications

                         GP90         GP90/03      GP90/23         GP11
Cartridge            7.5x53.5        7.5x53.5     7.5x54.5       7.5x55

Case Length            2.106"           2.106"        2.15"       2.185"

Rim Diameter            .492"            .492"          .5"        .496"

Head Diameter           .488"            .488"        .496"        .493"

Neck Diameter           .362"
(w/ paper patch)        .362"
(w/ paper patch)        .328"            .335"
Bullet                  211gr           211gr        190gr        174gr
                        Paper           Paper         CuNi         CuNi
                      patched         patched     Jacketed     Jacketed spire-point boat-tailed
                 steel-capped    steel-capped   round nose  
              lead round nose lead round nose
  
Bullet Diameter        .3208" 
(w/ paper patch)       .3208"
(w/ paper patch)       .3075"           .3086"

Bullet Length           1.14"            1.14"      1.165"         1.378"

Muzzle Velocity      1968 fps         1980 fps      2050 fps       2560 fps

Powder Measure        27-31gr            31gr       33.7gr       49.35gr 
                  Semi-Smokeless  Semi-Smokeless   Smokeless     Smokeless
                    Powder (PC88)   Powder (PC88)     Powder        Powder

Max. Chamber Pressure 36,970 psi      36,970 psi    38,390 psi   45,500 psi