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The rifle was the only Collier second model flintlock rifle of its kind held in public collections around the world, museum staff said.
This particular rifle is also believed to have the longest verifiable provenance of any known Collier rifle, having reputedly been owned by former Ngai Tahu paramount chief Tuhawaiki.
Hone Tuhawaiki became prominent within Ngai Tahu after warfare with North Island-based Te Rauparaha during the 1830s, and became known as a fierce and charismatic leader.
Dr Nicholson, of the School of Art Institute in Chicago, inspected the rifle, apparently made in 1824, at the museum recently and discussed "what's so wonderful about this particular object''.
A gun firing five rounds was clearly "a big deal'' when single shot firearms were the norm, he said. It was also "exceptionally important in the history of manufacturing.''
Dr Nicholson, who is writing a book on the Collier guns, said the rifle stock was handmade, but the revolving chambers were mass produced.
The firearm thus reflected the wider move from handmade items to the mass-produced parts required by a consumer society.
Tuhawaiki was based on Ruapuke Island, southwest of Bluff, and signed the Treaty of Waitangi in June 1840.
He later drowned in October 1844 near Timaru, after a large wave swept him off his boat.
Waihola resident Melvin Cain, a descendant of Tuhawaiki, met Dr Nicholson at the museum, and said Tuhawaiki's prowess as a warrior had also been historically important in helping protect all the people south of Banks Peninsula from raids by northern iwi and led by Te Rauparaha.