The death of Pc Ian Terry at a police firearms unit training exercise was an "accident waiting to happen", an instructor said.
Another instructor told the inquest into his death that the role play was "dangerous".
The Greater Manchester Police (GMP) officer, from Burnley in Lancashire, was shot in the chest by a colleague in June 2008.
The father-of-two was not wearing any body armour during the exercise, at a disused factory in Newton Heath, in which he played a fleeing suspect.
He was shot by a colleague - only known as "Chris" - who had the job of shooting out the tyres of the suspect vehicle, in which Pc Terry was a passenger.
He told Manchester Coroners Court that on seeing Pc Terry holding an unloaded gun, he acted "instinctively" and pulled the trigger on his Remington 870 pump action 12-bore shotgun.
Chris admitted he broke one of the "golden rules" by pointing his loaded weapon into the car carrying Pc Terry.
Chief Constable Peter Fahy apologised for GMP's failure to keep Pc Terry safe
During exercises, including the fatal one, firearms officers repeatedly defied instructions never to raise their shotguns, the inquest heard.
CCTV footage showed that officers raised their weapons and pointed them at colleagues, despite being ordered not to.
The instructor in charge of the exercise, known as "Francis", said the use of paintballs as ammunition was cancelled during training the week before because one of the student officers complained that they would "sting" if he was hit.
Francis said he wanted to make the specific tactic to catch serious criminals in a getaway car "more realistic" but admitted the drill was inherently dangerous.
He introduced live shotgun rounds, paintballs and a "shoot scenario" where his students were unaware the officers playing the roles of fleeing villains would be armed with unloaded guns.
He told the inquest he believed the control and safety measures already in place were sufficient and the officers involved were experienced and professional, but admitted he was "too trusting" that they would follow the rules.
A second instructor, known as Keith, who described the exercise as an "accident waiting to happen", said mixing two different kinds of ammunition and a role-play exercise with a potential shoot-out was inadvisable.
He said it was "very naive" to think instructions and the experience of the officers alone would be enough to prevent the fatal incident.
Keith, who had carried out a similar training exercise the week before, was stood down by Francis on the day of the drill.
GMP said changes had been made since the fatal shooting
Jurors heard Keith had a reputation for doing things "by the book" and was considered by some in the training unit as a "block to learning".
A report on the incident by the National Police Improvement Agency (NPIA), a force watchdog, reached damning conclusions.
Risk assessments to ensure safety were "vague and inconsistent" and "simply not fit for purpose", it said.
GMP Chief Constable Peter Fahy has apologised for the force's failure to keep Pc Terry safe, and said he accepted some of their practices and systems contributed to his death.
He added: "Since Ian's death GMP has made a number of changes to policies and re-enforced existing policies to ensure training exercises are carried out in the safest way possible.
"As a force we need to continue to carry out firearms training if we are to keep the public in Greater Manchester safe. However, we need to do everything we can to ensure this training is delivered safely, and everything possible is done to minimise the risks involved."
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