Police experts have criticised the reported introduction of a “less lethal” gun attachment by the Ferguson police department, nearly six months after the fatal shooting of unarmed teenager Michael Brown.

Named “the Alternative”, the bright orange attachment sits on top of a pistol, positioning a ball-shaped projectile over the barrel of the weapon. This allows the first bullet fired to meld with the ball projectile to create a “less lethal” round designed to incapacitate a target but not pierce the skin. After this first round, the gun then fires as normal.

“The result,” claims the device’s creator at California-based Alternative Ballistics, “is serious pain with less internal injury to the body than a conventional bullet.” Officers would be encouraged to carry the attachment and place it on the weapon before discharging.

The Washington Post reported that the technology will be trialled by five Ferguson police training officers this week, after the department’s assistant chief, Al Eickhoff, began examining the use of “less lethal” technology in the wake of Brown’s shooting.

“It gives another option,” Eickhoff, who has tested the device personally, told the paper. “I really liked it ... You are always looking to save a life, not take a life.”

But experts have criticised the technology, arguing that placing an attachment over a weapon used for lethal force “muddies the water”.

“We know that when we pull and use our firearms, it’s of great likelihood that someone is going to die. Now we’re talking about a device that you attach to the front of a gun to use for ‘less lethal force’,” said Major Neill Franklin, a 34-year police veteran and former commander of the training division of Baltimore city police. “We should not commingle lethal force with less lethal force. It becomes confusing and very problematic.”

Franklin, now the executive director of the advocacy group Law Enforcement Against Prohibition, continued: “It’s only one shot. We don’t train to shoot once like that, most police agencies train to shoot two shots very quickly because a lot of times the first shot may be off target.”

He told the Guardian that implementing the device would require “extensive retraining”.

In a statement, the Ferguson police department said the technology had been demonstrated to department officials, but no decision on its implementation had been made.

Alternative Ballistics’ chief executive, Christian Ellis, told the Washington Post that the device has not yet been trialled on a human body but has been tested on foam, gel and leather chamois.

Alternative Ballistics did not respond to questions from the Guardian on how many other police forces were trialling the technology and what safety testing the device had been subject to.

The executive director of Amnesty International USA, Steven Hawkins, said in a statement to the Guardian that any use of technology should be strictly controlled and follow a thorough safety review.

“Amnesty International recognizes the importance of having available a range of tools to minimize the risk of death and injury inherent in police use of firearms,” Hawkins said.

“We have concerns, however, about the way so-called ‘less than lethal’ weapons may be used, which can result in serious injury and sometimes death.” Hawkins drew attention to the fact that between 2001 and 2012, more than 500 people in the US have died after being shocked with Tasers.

“Accordingly, there should be a safety review of these weapons before they’re handed to officers in Ferguson, or anywhere else, and related policies must be in line with international standards for the use of weapons,” Hawkins said.

The move comes as the White House confirmed a $97m injection for the president’s Community Policing Initiative at the 2016 federal budget on Monday. The initiative aims to “build and sustain trust between law enforcement and the people they serve” in the wake of the Ferguson shooting.

The grand jury decision not to indict officer Darren Wilson, who shot the 18-year-old Brown in August, along with the grand jury decision in Staten Island not to indict an officer who placed another unarmed black man, Eric Garner, in a banned chokehold before his death sparked protests across the US.

The Community Policing Initiative will provide funding for the implementation of body cameras on police. Brown’s parents have called for the mandatory implementation of body cameras in all police forces around the US.