The death of soldier Private Sean Benton at Deepcut Barracks in 1995 was caused by "self-inflicted" gunshot wounds to the chest and has been formally recorded as a suicide.
Coroner Peter Rook QC was concluding at an inquest at Woking Coroner's Court, where he said:
"I'm satisfied that the fatal wounds were self-inflicted."
He said the first round injured the soldier, but that a second round - fired by Pte Benton when two officers arrived at the scene - proved fatal.
Notes to his friends and family were found afterwards.
Summing up, the coroner said:
"There was ample evidence available to those at Deepcut that Sean was vulnerable."
Pte Sean Benton, 20, was found with five bullets in his chest at the Surrey base in June 1995, shortly after he had been told he was to be discharged from the military.
He was the first of four soldiers to have died there between 1995 and 2002 amid claims of bullying and abuse.
Privates Sean Benton, Cheryl James, Geoff Gray and James Collinson all died from gunshot wounds at Deepcut. (Image: PA)
Mr Rook described a litany of failures with the original investigation into Pte Benton's death.
He said he was hampered by a failure to preserve evidence, poor photographs of the scene and a lack of scrutiny of eyewitness accounts, among other things.
He said: "Even by the standards of 1995, the investigation into Sean's death was woefully inadequate.
"My own investigation has been greatly hindered by the inadequacies of the original investigation."
The court heard how Pte Benton had changed in attitude during his time at the barracks.
The coroner said: "A common theme from former trainee colleagues is they observed a change in him ... he was not as bubbly as he used to be."
A witness previously told the inquest: "Sean was initially happy and as time went on he laughed less ... he just stopped caring."
This included a change in his demeanour and his appearance after he failed a military driving test, the court heard.
Fellow recruits described Deepcut as an "oppressive place".