This is where it both begins and ends. The 12,7x42R is the first cartridge with a metallic case to be adopted by the Swedish military and the last of the old style to be used. It had a big bore and a slow bullet in a rim fire case not unlike that of today’s .22LR cartridge. The caliber was already outdated at the time of introduction as it was considered as being too large and too slow to have the velocity and range necessary for a military cartridge. With a velocity of only 385 meter per second, it was about as slow as muzzle loading rifles that it was replacing. The Franco-Prussian War of 1870 -71 quickly proved this type of ammunition to be outdated by more modern centerfire cartridges and the caliber was once more in debate.
The selection of the 12,7x42R cartridge and, indeed, the Remington design was driven by the fact that some 30,000 recently funded and acquired m/1860, m/1864, and m/1860-64 now obsolete rifles were at hand. So at not to make waste of such an expensive investment, it was determined that these rifles could be economically converted to the Remington design and thus salvaging many of the parts. As all three of these obsolete rifles were in the 12,7mm caliber, a cartridge was quickly adapted so the barrels of the rifles could be reused in the conversions as well as the new manufactured m/1867 rifle.
Over the years of service and in the times since, this particular cartridges has been referred to in many ways including: 12mm, 12,17mm, 12,7mm, etc. The 12,17 measurement was the original designation based on the measurement between the lands of the bore’s rifling. The 12,7 measurement, which is taken between the grooves,of the rifling, is the modern way to correctly specify the caliber of the bore.
The cartridges were always issued in paper wrapped 10-round packages. The package labels never state the caliber but only that the cartridges were intended for the m/1867 rifle.
Utdrag ur vapenlära, Sixten Schmidt, 1909.
Arméns Eldhandvapen förr och nu, Josef Alm, 1953.