Paul Metcalfe said he was minding the gun for unnamed criminals
A teenager has been jailed for three years after his father told police he had found bullets in his son's bedroom.
Paul Metcalfe's father discovered 11 bullets in the room and called police - who also found a handgun under the bed.
The 19-year-old, of Hibson Road in Nelson, Lancashire, pleaded guilty to possession of a weapon and the ammunition at Burnley Crown Court.
His father Neil Metcalfe, 43, said he had "no regrets" about his decision to call the police.
"I would think for longer, knowing what I know now. I only found ammo - I didn't know the weapon was there and I didn't know he was facing five years.
"Of course there's guilt that he will be locked up for so long and I feel sorry for him."
His son said he was "minding" the bullets and gun for criminals whom he refused to name.
The minimum sentence for possession of a firearm is five years in prison.
But Judge Christopher Cornwall took into account the fact his father informed police - the defence argued a longer sentence might otherwise deter other public-spirited parents.
Neil Metcalfe says he is disappointed by the sentence
Mr Metcalfe said the sentence was unfair.
"The judge has said three years - I was hoping for two.
"He hadn't even touched the gun - the police said that before. It was bagged and sealed.
"He did not go down the street threatening anyone with a gun. He had no intention of using it and should have only got about 18 months - people get less for GBH."
In a statement to the court, Mr Metcalfe said he believed his son had fallen into the wrong circle after becoming involved in the drug sub-culture as a cannabis user.
Judge Cornwall said cannabis may have "acted as a gateway from the respectable world your parents intended to the foul and dangerous world of drugs".
Sentencing him, the judge said: "The grim reality is that the pistol you were looking after was capable of firing live rounds.
"Your intention was to return this lethal weapon to dangerous men who were intent on using the gun to achieve their criminal aims."
In my view the three year sentence is fair
Det Insp Derek Jones
Mr Metcalfe said were he to do it again he would have accompanied his son down to the police station - something the judge might have given him more credit for.
The semi-automatic gun was originally a blank-firing weapon which had been converted to fire live rounds.
Detectives still do not know where the gun came from and said they were striving to find out.
Neil Metcalfe backed his son's decision not to tell officers where he had got the gun, because of possible reprisals which would "turn his three-year sentence into a life sentence".
Paul Metcalfe will serve half his sentence in a young offenders' institution and the remaining half on licence.
Det Insp Derek Jones, of Lancashire Police, said: "In my view the three-year sentence is fair, but Paul Metcalfe has received a slightly lesser sentence because of the commendable actions of his father.
"I would like to remind people that the mandatory minimum sentence for possessing a firearm, under normal circumstances, is five years.
"Handing his son in to the police must have been an incredibly difficult decision for Mr Metcalfe to make, but it was certainly the right one and if he hadn't the consequences could have been horrific."
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