Andrew Bourke, 25, had been drinking in The Crown in south Acton, west London, since early afternoon and was looking for trouble by the time Ian Dyson called in at 10pm for a drink, the court was told.
Mr Dyson, 48, who lived on a south Acton estate near his only daughter to whom he was devoted, was challenged to a fight by the younger man but ignored him.
Bourke, a building worker who lived in Conrad Tower on the same estate, left the pub saying he was going to 'sort out the whole manor'.
He went to his grandparents' home and returned moments later with a First World War pistol.
John Nutting, for the prosecution, said: 'There was a bulge in his jacket. He walked up to where Mr Dyson was sitting and stood in front of him.
'He pulled aside his jacket and revealed he was holding a revolver in his hand.
'Dyson looked at the defendant. He slowly lowered the gun at the victim's head and pushed the barrel towards Dyson's mouth. Nothing was said.'
Mr Nutting continued: 'Then he pulled the trigger at point-blank range. The bullet went into Dyson's mouth and struck the back of his throat, shattering bones and fatally injuring him. He remained upright for a few minutes in his seat.'
Bourke, still holding the gun, looked 'menacingly' around at the other drinkers in the pub. Mr Nutting told the jury it was as if to say: 'If you dare to give an account of what happened here . . .' '
Mr Dyson died soon afterwards from his injuries. Bourke went on the run after the killing and was arrested in February this year using a false name and living in Birmingham.
He told the jury he did not know the gun was loaded. He was cleared of murder but convicted of manslaughter .
Mr Justice Mantell told Bourke, who has previous convictions for violence and dishonesty: 'You are two people, the man you are now standing before me, but when you are drunk you are a bar room bully.'