U.S. activists often point to New Zealand, the UK and Australia to show what's possible when it comes to gun control, but experts say those countries' examples are hard for the United States to emulate.

Pro-gun rally, organized by Gun Owner's Action League of Massachusetts on Boston Common in Boston, MA on April 3, 2013. Rick Friedman | Corbis | Getty Images

Gun control is at the forefront of the national debate in the United States — again — after a weekend that saw 29 people massacred in separate incidents in the states of Texas and Ohio. In the wake of mass killings there and in places such as Marjory Stoneman Douglas High School in Parkland, Florida, last year, the call for reforms — such as raising age limits for gun purchases, expanding background checks, or banning assault weapons — has grown louder. But outright gun bans of the sort undertaken by the United Kingdom, Australia or New Zealand are much more difficult to implement in the United States.

'There is a legal headache'

New Zealand last year banned "military-style" firearms after a mass murderer used such weapons to kill 50 people in attacks on mosques in Christchurch. In the U.K., a mass shooting in Dunblane Primary School in Scotland in 1996 left 17 dead, including the shooter. The government reacted by banning all handguns — more powerful weapons had already been banned previously — and held a gun amnesty that collected more than 162,000 handguns. A gun amnesty lets people hand over weapons that may have been obtained illegally, without the fear of prosecution. Since Dunblane, only one mass shooting has taken place in the U.K., when 10 were killed in Cumbria in 2010.

Prime Minister John Major with wife Norma lays floral tribute at Dunblane after the shooting tragedy on March 17, 1996. Tim Graham | Corbis | Getty Images

A massacre of 35 people in Tasmania in 1996, the worst mass shooting in Australia's history, led to an almost immediate response by the country. The government implemented a ban on semi-automatic and automatic weapons, and also held a gun amnesty. A subsequent amnesty held last year saw Australians hand over more than 57,000 guns. The country hasn't had a mass shooting since the massacre in 1996. Countries such as the U.K and Australia can implement such policies, however, because they do not have a constitutional right to bear arms, Darrell Miller, a professor of law at Duke University, told CNBC last year. "These are countries that don't have Second Amendment right to arms, so there's no constitutional right that has to be addressed with respect to gun reform policies of any type, whereas in the U.S., there is a legal headache," Miller said. "The Amendment forbids similar measures."

Members of the audience listen at the National Rifle Association (NRA) Leadership Forum in Atlanta, Georgia on April 28, 2017. Jim Watson | AFP | Getty Images

The pure number of guns floating around in the United States presents its own challenges. "We are a country with over 300 million guns in civilians' hands right now," Eric Ruben, a fellow at the Brennan Center for Justice, pointed out in 2018 following the Marjory Stoneman Douglas killings. "I don't see us becoming like other European countries without guns, but I would not be surprised if public sentiments shift as more shootings occur in the U.S."

The NRA

Supporters of gun control also face strong opposition from the National Rifle Association — arguably the most powerful lobby group in the country. "The NRA are a powerful counterweight to mass mobilization, even to sympathetic movements like the ones these kids have," Miller said, explaining that the NRA's members maintain a passionate dedication about guns and gun rights, more so than the individuals who want limitations on guns. An April report in the New Yorker indicated that the NRA has run into financial trouble this year.

States may be the place for activists to start