.303 British

We hear lots of stories about soldiers picking up an AK-47 on the battlefield and using it in preference to their own, small-caliber rifle, but here's a twist on the yarn, from Takedown: The 3rd Infantry Division's Twenty-One Day Assault on Baghdad, just out from Naval Institute Press. Quoting Sgt Dillard Johnson:

"When he is about thirty-five meters away he aims the rifle at us so we killed him with the coax. His rifle was a really nice .303 British so I kept it for a while. Later in the war I was shooting RPG guys from 200 plus meters away. When that .303 hit them they stayed down for good."

My dad bequeathed me a .303 "jungle carbine" that he used for hunting pigs in Arizona. In 1920 he'd employed essentially the same weapon to snipe at the Royal Irish Constabulary barrack in Ballinhassig, County Cork, and that Enfield of course was a veteran of WW1. What other weapon has had a service life half as long?