Instead it is handguns that are walking out the door. "Glocks, Smith and Wesson revolver, anything they can fit in their hand," he says.

Self-defence ammunition – hollow point rounds designed to break apart when on impact with a body to inflict maximum damage – is walking out the door too.

Other gun shops in the area are reporting a similar surge in sales driven by fears of another wave of rioting over the shooting by a white police officer, Darren Wilson, of an unarmed black teenager, Michael Brown, in August.

Tensions have increased as a grand jury is expected to decide soon whether or not  Mr Wilson should be formally charged over the shooting.

Many fear that should he not be charged riots could again break out.

As some in the area stock up on arms, activists, rallying under the slogan "Hands Up, Don't Shoot" have been preparing their tactics for street protests, while authorities have been training extra police and stockpiling riot gear.

Mr Brown, who was 18, was shot dead after Mr Wilson stopped him as he and a friend walked along a street in the city of Ferguson on the fringes of St Louis. Accounts of what happened differ. Mr Wilson claims Mr Brown assaulted him through the window of his squad car before fleeing, only to turn and begin to charge back at him. He shot Mr Brown six times. Other witnesses say Mr Brown was standing with his hands in the air when he was shot dead.

The shooting and heavy-handed police response to community protests soon spiralled into riots as the majority-black population vented its frustration at the majority-white police force.

People across the country were appalled over subsequent days by the sight of police officers with military weapons and vehicles forcing protesters and reporters from streets.

Eventually the state governor, Jay Nixon, ordered state police to take control  and the Federal Department of Justice began investigations into civil rights violations. The riots were replaced with an ongoing peaceful protest movement.

Activists have maintained a presence on Ferguson streets  since, determined to draw attention to what they believe is a culture of police violence against African-Americans, particularly young black men, in Ferguson and across the nation.

Tension has slowly increased throughout the grand jury's investigation due to the perception that authorities are determined not to indict – or lay charges – against the officer.

It is believed a decision could be made very soon.

Protesters claim the prosecutor in the case, Robert P. McCulloch, whose father was a St Louis police officer who was killed by a black man in the line of duty, has a long history of siding with police officers in similar cases.

Despite early rumours that Mr McCulloch would recuse himself or be replaced he has stayed on the case, although he has delegated the presentation of evidence to two senior attorneys from his office.

Sceptics of Mr McCulloch point out that his office is not recommending a specific charge against Mr Wilson, allowing the jury to decide if sufficient evidence exists for an indictment. Without a charging recommendation, the grand jury can return  first or second-degree murder, or either voluntary or involuntary manslaughter, or no indictment at all.

Many protesters also believe the public is being prepared for a finding in favour of the officer by a series of leaks from the grand jury's investigation.

The New York Times reported that Mr Brown's blood was found on Mr Wilson's uniform and inside his police car, supporting testimony that there was an altercation in the police car.

If there is no indictment, Adolphus Pruitt of the St Louis chapter of the African-American advocacy group, the NAACP, told CNN: "As a community, we are going to be thrust right back into the same discontent and civil disobedience we experienced the first time around."

Another protester was even more blunt, saying: "If there is not an indictment, excuse my French, all hell is going to break loose."

Many activist organisers have been calling for peaceful protests and even running workshops on civil disobedience. Last week a leadership coalition representing 50 known groups asked authorities for 48 hours notice of the decision so they could try to avert violence.

Likewise, Governor Jay Nixon has declared the 1000 extra police who have been called in are being trained and equipped for their defence. According to a Guardian report the department has spent $US200,000 on 235 riot helmets, 135 shields as well as batons, shin guards and 2000 pairs of plastic handcuffs.

But the department has also stocked up on teargas grenades, "hornets nest" sting grenades, which blast out dozens of rubber bullets, as well as beanbag rounds and pepper balls, which resemble paintballs but are coated in an irritant, the paper reports.

The National Guard has been placed on standby.

Some of the protesters appear to be preparing for conflict too, with some posting pictures of homemade shields online.

Shermale Humphrey, 21, had been working at a Subway restaurant in St Louis when Mr Brown was shot, told the Washington Post that she considered herself a "revolutionary" and supported the right of protesters to express themselves by burning down a petrol station during the earlier riots.

When the paper caught up with her at a community centre she stood by a sign on which the protesters "Hands Up Don't Shoot" slogan had been ominously inverted to read simply, "Shoot back."