A soldier was found shot dead at Deepcut barracks in Surrey hours after telling colleagues he was thinking of killing himself, an inquest has heard.
Pte Collinson's parents said their son was happy with his life
Pte James Collinson, 17, from Perth, said he was considering killing himself adding: "I am going to do it tonight".
He later borrowed a rifle from a fellow recruit and walked off for a smoke, a jury at Epsom Magistrates' Court heard.
The hearing follows inquests into the Deepcut deaths of three other soldiers from Sussex, Wales and County Durham.
Monday's hearing heard Pte Collinson was not officially old enough to be alone on guard duty with a loaded gun.
He had appeared to have been in "good spirits" earlier that day when he spent time with his mother Yvonne.
But hours after being driven back to the Princess Royal Barracks he was dead.
Fellow soldiers heard a single shot ring out on the night of 23 March, 2002, shortly after Pte Collinson left, rifle in hand.
Moments later his body was discovered in a nearby wooded area with a close-range bullet wound to the chin, which had exited through the top of his skull.
Ambulance technician Graham Furlonger claimed he was told by one of two soldiers that, in a conversation with Pte Collinson on a minibus earlier that evening, he had indicated he was thinking about killing himself.
"I recall one of the soldiers saying something about the soldier who had died having spoken of harming or killing himself that evening.
"He (Pte Collinson) said, 'I'm going to do it tonight', or something like that," Mr Furlonger said.
"I heard that another soldier had given the deceased his gun and had gone off on the pretence of having a cigarette, and then shot himself."
The two soldiers on guard duty with Pte Collinson, Ptes Stacy McGrath and John Donnolly, were both represented by a lawyer.
Paramedic Roy Gaskin told the inquest he was accompanied at the scene by a corporal.
He said what "stuck in my mind" as he stood over the body was hearing a corporal comment that a court martial could follow the tragedy.
Clockwise from top left: Sean Benton, James Collinson, Geoff Gray and Cheryl James
Mr Gaskin said that the corporal had indicated that whoever had earlier signed out the weapon, which Pte Collinson borrowed, could be in trouble for allowing an under-age recruit to be alone with a loaded rifle.
Dr Simon Brown, who confirmed the death, said he spoke to two soldiers, who the court was told were Privates McGrath and Donnolly.
"I remember them being distressed by what they had seen," the doctor said.
"They were quiet and how you would expect of people who had just witnessed a tragic event."
'In good spirits'
Police and Army investigators concluded early on that no-one else was involved in the death, the court heard.
Pathologist Dr Susan Dodd said Pte Collinson had been in good spirits but that police had been satisfied no other person was involved.
Dr Dodd said Pte Collinson's parents had described their son as being happy with his life, telling her how he had dyslexia as a child and always stood up for himself and others.
The hearing heard that the soldier spent time with his mother in Reading, Berkshire, before returning to Deepcut that year, when he "seemed in very good spirits and was looking forward to Easter".
The inquest was delayed for four years due to long-running police inquiries.
It is being heard under Surrey coroner Michael Burgess who handled inquests into the three other deaths of Pte Sean Benton, from Hastings, Pte Cheryl James, from Llangollen, and Pte Geoff Gray, from Seaham.
The findings of an independent review into the deaths, between 1995 and 2002, are expected to be published by Nicholas Blake QC after this inquest.
Surrey Police's investigation was criticised in a review by Devon and Cornwall Police.
The families of all four soldiers continue to demand a public inquiry.