Jindal charged that Vice President Joe Biden and former Secretary of State Hillary Clinton, both possible Democratic presidential candidates, think the Second Amendment is little more than "a phrase from a speech writer."
"If they had their way they'd simply cut and paste the Constitution and just get rid of the Second Amendment entirely," said Jindal, who approved several gun rights bills last year, including one that creates stiff penalties for those who knowingly publish the names of gun permit holders.
Rubio opposed limiting gun rights after Sandy Hook, but he also saw his NRA grade drop from an A to a B+ amid criticism of his stance on some gun-rights legislation.
He said Friday that being able to provide a safe home for one's family is fundamental to achieving the American dream. And he said that while gun-rights supporters were outraged and saddened by violence such as Sandy Hook, public policy "must be guided by common sense."
"Making it harder for law-abiding Americans to defend themselves has not, does not and will not prevent future tragedies such as these," Rubio said.
Both Santorum and Pence noted their wives share their love of guns. Pence, who approved a measure this year to allow guns in locked vehicles on school property, said when he met his wife, she had a gun and a motorcycle and "it was love at first sight."
Santorum said it's not just gun rights that are under assault. He called on the NRA's millions of members to also fight for religious freedom and First Amendment rights.
"Just protecting the Second Amendment while all other freedoms falter isn't a winning strategy," Santorum said. "We need you to engage."
Among the more than 70,000 people expected to attend the three-day convention was Estel Rhoton of Lebanon, Ind., who made the trip with his wife and daughter. The 64-year-old union electrician said he thinks Jindal "could be presidential timber." But he liked them all.
"Any of these guys would be so far above what we've got now," Rhoton said. "It's not even close."
Gun-control supporters also were making their voices heard, holding rallies outside the event throughout the weekend. An Associated Press-GfK poll in December found that 52 percent of Americans favored stricter gun laws, 31 percent wanted them left as they were, and 15 percent said they should be loosened.
Two other Republicans considered possible presidential candidates, former Florida Gov. Jeb Bush and New Jersey Gov. Chris Christie, didn't attend.
Bush has attended the NRA's past conferences and has signed legislation supported by the group. In 2005, he signed the measure which allows a person to use deadly force when threatened in public places. The law received attention in the shooting death of Trayvon Martin in Sanford, Florida in 2012. Bush also supports instant background checks for gun-show gun purchases, an unpopular position with the NRA.
However, Bush has kept his distance this from such events and been selective making public political statements ahead of any announcement about his plans for 2016.
Christie has not been as popular with the NRA as Bush. In 2009, as a candidate for governor, he staunchly opposed a measure in Congress that would have superseded the state's strict laws forbidding carrying concealed weapons. That bill would have required New Jersey to recognize concealed-carry permits from out-of-state visitors to the state.
However, Christie has kept a lower political profile outside his chairmanship of the Republican Governors Association. Supporters say raising money for that group, and the GOP governors and candidates running this year, is consuming most of his political time.
He was in Seaside, N.J., on Friday, the site of some of the worst damage from the 2012 storm that ravaged the Jersey Shore.