The man swung the rifle across his shoulder like a hunter, picked up a bottle of whisky, and casually began walking towards the exit.
Lee jumped the counter and grabbed the offender, who swung round and smashed the rifle butt against Lee's head.
"That's when I knew it was plastic because he smashed it on my head. There was a little bit of pain but not really."
Lee pushed the man up against the wall and wrestled with him until he let go of the whisky bottle and fled.
North Shore area commander Les Paterson said the offender left his jacket, the plastic imitation gun and the bottle of whisky behind. They were all were brushed for fingerprints.
"It's normally advisable for store owners not to challenge armed persons," he said. "However, in this case the owner was able to deduce he wasn't dealing with Butch Cassidy."
The offender was arrested and charged with robbery. He is due to appear in the North Shore District Court next week.