Anybody interested in the period of the Mexican Revolution would do well to get a copy of Eileen Wellson's "The General and the Jaguar". It's a well-written history of the "Punitive Expedition", the American effort to catch or kill Pancho Villa in 1916 after his raid on the New Mexican border. Not much specifically on guns but a lot about the conditions of combat, showing about how the surviving weapons from that period got the way they are now. I'd say both the US Army and the Division del Norte were "rid hard and put away wet." Wet with sweat, as much an enemy of guns as blood and tears.
Armybrat's father's friend having a twin brother on the other side of the conflict is pretty characteristic of those times among The Neighbors. The "Revolution" turned into a long, bloody civil war very quickly.
Both of my gringo grandfathers were involved in that in various ways. One of them was a big supporter of Porfirio Diaz, the exiled dictator overthrown in 1910, for all his life. The other went into Mexico after Villa with Pershing. Neither ever talked about it, although I have both of their sidearms of that period, a Colt New Service .44-40 and a Smith and Wesson .44 DA .44 Russian. Not being guerrillas, they took very good care of their weapons--they show no neglect, just lots of leather time.