HOUSTON (AFP) - Keith Jehlen says the shooting at a Texas elementary school makes him "sick," but that "you can't blame the gun" used to murder 19 small children and two teachers.

"We've always had guns in this country," says the 68-year-old retired US Postal Service worker, noting that he personally owns more than 50 firearms.

Jehlen is standing in line to see former president Donald Trump speak at a National Rifle Association convention that is controversial being held just hours from Uvalde, the town where the school massacre took place earlier in the week.

Reflecting on the shooting, he grimaces and says: "It made me sick to my stomach."

But guns are not the problem, says Jehlen, who is dressed in camouflage shorts and a Trump hat. He argues that the disaster may well have unfolded differently if people at the school were armed.

"Killers aren't afraid of the judge, they're not afraid of the police," he says. "They should be afraid of the victim they're going after."

The NRA event - which lasts through Sunday - is being held in a vast downtown convention centre with anti-gun protesters gathered outside.

Democratic gubernatorial candidate Beto O'Rourke - who has routinely attacked his opponents for their inaction on firearms reform - addressed the demonstrators.

"Blood is on your hands," one protester's sign says.

"Guns = death," reads another.

In booth after booth in the cavernous hall, hundreds of firearms - all made inert with their firing pins removed - are on display, from small handguns to AR-15s, the ubiquitous semi-automatic weapon used by the gunman in Uvalde.

'This is not Australia'

Tactical gear, hunting equipment and clothing share space with gun accessories including high-power scopes, suppressors and 60-round magazines.

Retired law enforcement officer Rick Gammon eyes a wall of black semi-automatic rifles at the convention, saying any efforts to take firearms from Americans are doomed to fail.

"You'll never take people's guns away. This is not Australia," 51-year-old Gammon says as he looks at the Hellion rifles - a compact bullpup design that he notes would fit well behind his driver's seat or in his gun safe at home.

After the April 1996 Port Arthur massacre of 35 people, Australia enacted tougher new gun laws included a general ban on the use of semi-automatic rifles, shotguns and pump-action shotguns except for specific purposes.

America - plagued by far more frequent gun violence, but with the right to bear arms is enshrined in the Constitution - has repeatedly failed to take action after mass shootings.

"I'd love to see universal background checks," says Gammon, referring to a long-sought reform that has majority support in the United States.

"But it's not going to stop someone hell-bent on crime."

'Villainising a tool'

The convention is not just a gathering of gun enthusiasts, but also a place where they can test the "feel" of weapons they are considering buying.

"Oh I like this," Lisy V, 31, tells a gun manufacturer representative as she tests the weight and balance of a 9 millimeter pistol.

"You put it in purple too, and that got my attention," adds the military veteran, who is in the market for a new pistol that she can conceal in a holster under her skirt, because "it's too hot for pants in Texas."

But she turns contemplative when asked about Uvalde.

"Personally, I feel like there should be more gun education," she says, but with 18-year-olds able to join the military, the veteran believes they should be able to buy assault rifles as well.

"They can enlist, right? If they can enlist, they can shoot a weapon," she says.

Jim Maynard, a gun owner and industry advocate, says that while there is "a lot of uncertainty" in America today, and people are grieving, he agrees with the decision to not postpone the NRA convention.

"Villainising a tool doesn't address the problem that we're having," he says.

People blaming guns for America's violence crisis was just "hype," and they should focus more on expanding mental health programs.

"The protest outside does zero for preventing the next shooting from happening - and it's not going to stop a person from committing violence," Maynard adds.