A POLICE constable shot his colleague in the buttocks while trying to demonstrate that an unloaded gun could not go off accidentally, the High Court heard yesterday. Wong Nai-yuen, was unaware that a live bullet was still in the chamber of his service revolver when carrying out the demonstration, the court was told. The 22-year-old officer had been acquitted by Magistrate Hugh Sinclair in Tuen Mun Court in October last year of reckless use of a firearm in a manner likely to injure a person. Mr Sinclair said although Constable Wong had pulled the trigger deliberately, the discharge was unintentional and he had shown no malice. But the Crown yesterday sought to challenge the decision to acquit, on the grounds that the magistrate erred in going into the issue of recklessness after finding that Constable Wong pulled the trigger and discharged the firearm. The appeal court's Mr Justice Barnett reserved his judgment. Constable Wong and Constable Chan Ka-po, 25, were discussing the accidental discharge of police firearms at about 7.30 pm on October 13 in the report room at Tai Hing station. Constable Wong told his colleague he did not accept an unloaded revolver could ''go off''. Seeking to prove his point, he drew his own gun, then took out the bullets and put them in his pocket. He then pulled the trigger, asking his colleague: ''How can it go off with no bullet?'' But before he finished his sentence, a bullet was discharged, hitting Constable Chan on the buttock. Constable Wong said he had drawn the revolver, unloaded it and pulled the trigger very swiftly, and had thought all six bullets had been removed. He said he did not aim his gun at anything, nor had he deliberately fired at anyone. Mr Sinclair last year held that Constable Wong believed his revolver was empty when he pulled the trigger. While he was careless in failing to ensure all six rounds of ammunition had been removed, he had not acted recklessly nor he had intended to injure anyone. Seeking to overturn the magistrate's decision, Darryl Saw, for the Crown, submitted that the circumstances in which the bullet was discharged were sufficient to establish the count laid against Constable Wong. But having found it as a fact, he said, the magistrate erred in bringing in the element of recklessness and wrongly attached it to Constable Wong's action rather than intention. Recklessness had no place in the offence and the magistrate should have addressed his mind to the issue of ''in a manner likely to injure'', counsel submitted. Keith Oderberg, for Constable Wong, argued that the issue of discharge had two elements: intentional or possible recklessness in letting the revolver go off. But for that to be relevant, the person who let it go off would have to have known there was a live bullet in the chamber of the gun, or have been reckless as to whether there was. Mr Oderberg said the magistrate had been satisfied that Constable Wong had honestly believed the gun was empty, and that he had not been reckless. Mr Sinclair's finding was entirely proper, said counsel.