Mechanism

These type of mechanisms had been successfully used in past weapons, but only in machine guns designed by Hiram Maxim, John M. Browning and others. The famous Browning 1919 machine gun is an example of a very reliable weapon of war using a pull-back feed mechanism. The first attempt at pull-back feeding in a pistol was done in the Mars pistol, just before the turn of the 20th century. Unfortunately, the gun suffered feed errors and failed in military qualification. Other pistol designs that located the magazine under the barrel chamber were the "blow-forward" designs that arose between 1896-1925. The principle of operation consisted of an undependable force moving the barrel forward, exposing the top of the magazine, and various methods of allowing a cartridge to rise up in line with the barrel without having it fly out of the breech area. Although novel, these designs were said to have reliability issues.

The Boberg XR9 differs from prior pistol technology in that the cartridge is positively controlled from the time it is extracted from the magazine until the empty case is ejected from the breech area. Even a poorly designed lift mechanism would feed cartridges somewhat reliably when using stopping against the inside top of the slide.  However, the Boberg XR9 uses both kinematic balance of the cartridge and the top stop to provide complete and redundant control over the cartridge as it is picked from the magazine, lifted to be in-line with the barrel, and placed into the chamber.