If I remember, the water cooled Browning machine gun came of the US troop train that the Boys hijacked for the Springfields and the ammo to give to General Mapachi(sp).
Either the Colt 1895 or the Benet-Mercie machine gun should have been used instead of the 1917 Browning. However, it was/is a lot easier for prop departments to find watercooled Brownings than Colts or Benet-Mercies. Besides, only gun people would know the difference.
During the time of the Mexican Revolution and up through WWI, there was a good amount of German interest in Mexico. The US military was quite concerned that the Mexicans would join the Germans during the war and launch a military offensive along the border.
The German "observers" in the film made at least one misstatement when they questioned Pike about the pistols, they said something in the order of, "How did you get those pistols? They have not been released by your government yet." Colt was churning out the M-1911 for both the military and civilian market from the time the pistol was adopted.
------------------
Ne Conjuge Nobiscum
"If there be treachery, let there be jehad!"