Just what I was about to point out. The difference between firing a blank round and a live round is immediately discernible and dramatic. The only way a shooter wouldn't know the difference is if they'd never fired a rifle before at all.
Two items about that: first, the good news, that nobody on the Gilmore firing squad noticed any difference at all.
Uh...second, the bad: that Gilmore's brother said he found five holes in the shirt. Hmm...