The soldier has admitted failing to comply with written orders by storing the firearm, but pleaded not guilty to all other charges.
Ms Mason said her client was not aware the items he attempted to sell were Army property.
"He had personal items identical to the charging handle and the JPoint sights and he was very clear that the items he was selling were his own, not military property."
Evidence would show the pistol holster had been disposed of by the Army, she said.
He did not know the items found in the garage - Semtex, thunderflashes and ammunition - were stored there.
Prosecutor Captain Mike Mercer said the case was about a "highly trained soldier who did not comply with Defence Force orders or expectations".
He said the court would hear evidence that the items were property of the Defence Force and had been stolen by the soldier.
The first witness for the prosecution, a sales assistant at the Serious Shooters gun shop in Penrose, described how he was approached by the soldier about selling military items.
When he saw them he was concerned that some appeared to be current-issue military gear and forwarded an email from the soldier to a contact at Papakura Military Camp.
When asked by the prosecution why he was concerned he said some items were available only to military, and some appeared to be in Defence Force bags and have military stickers.
Under questioning from Ms Mason, he said the items would be available to the public in the United States.
