A man who caused panic by walking into a Walmart with a rifle and body armour told police he was testing his right to bear arms in public.
Dmitriy Andreychenko entered the shop heavily armed, days after a mass shooting at another of Walmart's stores.
"I wanted to know if that Walmart honoured the second amendment," the 20-year-old told police after his arrest.
Prosecutors have charged him with making a terrorist threat.
If found guilty, the charge could result in a four-year prison sentence and a fine of $10,000 (£8,300), Greene County prosecutor Dan Patterson said in a statement.
On 8 August, Mr Andreychenko entered the store "armed with an AR-style rifle slung across his chest", police said, wearing a ballistic vest and recording himself. Both the rifle and a handgun he carried were loaded.
He told police he did not expect the reaction his walk generated.
"This is Missouri, I understand if we were somewhere else like New York or California, people would freak out," he said, according to police filings.
The police statement also revealed that his wife, Angelice, had told him "it was not a smart idea".
"She told him that people were going to take this seriously due to recent events... she told him he was just an immature boy," it said.
His sister Anastasia also told police he had asked her to record video of what he called his "social experiment".
"She told him that it was a bad idea and that she did not want to do that," it said.
The store manager "believed Andreychenko came to the store to shoot people", the police statement said and triggered the fire alarm to evacuate customers.