Yeah I justl looked it up on Wikipedia:
"While an experienced marksman can tell the difference between a blank and a live cartridge based on the recoil (the blank will have lower recoil), there is a psychological incentive to not pay attention and, over time, to remember the recoil as soft. In more recent times, such as in the execution of Ronnie Lee Gardner in Utah in the United States in 2010, a rifleman may be given a "dummy" cartridge containing wax instead of a bullet, which provides a more realistic recoil"
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OneSullenBrit *air sandwiches*, Mon 21 Jun 2010, 15:39,
Reply)