Only one live round for a firing party?

Bollocks!

In the Great War, firing squads had one blank round loaded into one of the rifles, so everyone could kid themselves that they didn't fire the fatal shot. Unfortunately anyone who has done any shooting will know immediately from the recoil if they've just loosed off a blank, so the practise was rather pointless.
It's documented in Martin Middlebrook's excellent "The First Day on the Somme", recounting the testimony of Private Paddy Kennedy, 3rd Manchester Pals, 30th Division.