The GP11 was loaded with a 174 grain spitzer bullet and could reach 2640 fps. The diameter of the bullet was increased from the original design, also the length of the case was increased, to 55 mm. The GP11 generates around 45,500 psi of pressure. Older Schmidt-Rubins were converted to fire the GP11, and the round saw service with the 1911 series, the K31 series, and the Stgw 57 series, remaining in service until the mid-1980s. Due to the greater pressures produced by the GP11 round, it is not safe to fire GP11 rounds in Model 1889 Schmidt-Rubins!!! In addition to the standard FMJ 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 .2" of steel plate at 550 yards. Tracer rounds burn out to 880 yards, and can be identified by their red bases. However, most Swiss match shooters use standard GP11 ammunition, a testament to the accuracy of the GP11 round. As a curious side note: according to an article on Cruffler.com. The Swiss GP11 bullet strongly influenced the design of the M1 .30-06 round. By collani@collani.ch 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.