Cage reportedly walked off set screaming at her when she fired a gun without warning for the second time in three days.
The movie's key grip Stu Brumbaugh told The Wrap that Cage yelled, "Make an announcement, you just blew my f***ing eardrums out!"
Brumbaugh himself told the assistant director that the armourer "needed to be let go".
"After the second round, I was pissed off. We were moving too fast. She's a rookie," he said.
Gutierrez-Reed would apparently walk on to set with live rounds or blanks without telling the cast and crew. She also walked around with pistols tucked under her arms so that they were pointing back at people.
Before the fatal Rust shooting, the young armourer admitted that she hadn't felt ready for the responsibility when she accepted The Old Way job.
"It was also my first time being head armourer … I was really nervous about it at first, and I almost didn't take the job because I wasn't sure if I was ready," she revealed on a podcast last month.
"I think the best part about my job is just showing people who are normally kind of freaked out by guns how safe they can be and how they're not really problematic unless put in the wrong hands."
Brumbaugh went on to blame film producers for putting inexperienced people in important roles to save money.
"As producers refuse to bring more experienced people because their rates are higher, they demand we take our time and [producers] don't want to pay it. So they hire a newbie who is energetic and wants the job and will do it with less people," he said.
Neither Gutierrez-Reed or representatives for Cage could be reached for comment.
