Two owners of allegedly defective Remington Model 700 rifles say they will seek to block a landmark class action settlement approved by a federal judge last month, arguing the agreement does not go far enough. That means the fate of as many as 7.5 million allegedly unsafe guns is once again in question.

The settlement covers the iconic Model 700 and a dozen other Remington models with similar designs. In 2010, CNBC investigated allegations Remington covered up a deadly design defect that allows the guns to fire without the trigger being pulled. Remington has steadfastly denied the allegations and maintains that the guns are safe, but said it was settling the class action case to avoid prolonged litigation. Remington has agreed to replace the triggers in millions of the guns free of charge, and provide product vouchers for models it says are too old to be retrofitted.

But Lewis Frost, a deputy sheriff in Louisiana who owns three Model 700s, and Richard Denney, an Oklahoma attorney who also owns three 700s, have argued that the settlement's mechanism for notifying the public deliberately downplays the alleged risks the guns pose, and doesn't do enough to get word out about the replacement offer. Attorneys general in nine states and the District of Columbia made similar arguments in court. As of mid-February, only about 22,000 owners had filed claims to get their guns fixed.

Last month, U.S. District Judge Ortrie D. Smith in Kansas City dismissed the arguments and approved the settlement. While Smith said he was "concerned" about the low claims rate, he concluded that Remington and plaintiffs' attorneys had made "reasonable" efforts to notify the public. On Thursday, Frost and Denney said in a court filing that they are appealing the ruling to the 8th U.S. Circuit Court of Appeals. The filing does not describe the specific grounds for an appeal.

An attorney for the plaintiffs in the class action case, Mark Lanier, called the appeal "so sad," and said in an e-mail that it has "no chance of success."

"In the meantime," Lanier wrote, "millions of guns will remain unfixed while these professional objectors try to hold up the process to make some money."

As part of their appeal, Denney and Frost seek to block the $12.5 million in fees Smith awarded to Lanier and his fellow plaintiff attorneys. In response, Lanier says the plaintiffs will now try to recover additional fees from Frost and Denney to cover the cost of litigating the appeal.

Attorneys for Frost and Denney did not respond to requests for comment, nor did attorneys for Remington.

The impact on owners who have filed claims or were considering filing claims is unclear. Lanier said the process would stop while the appeal is pending. But as of Thursday afternoon, a special web site containing settlement information and claim forms was still operating, with no mention of the appeal.

The settlement covers Remington rifle models 700, Seven, Sportsman 78, 673, 710, 715, 770, 600, 660, 721, 722, 725, and the XP-100 pistol.