In the week after the nation's deadliest high school shooting in Parkland, Sen. Marco Rubio said he was open to limiting the size of magazines, the spring-loaded devices that feed bullet cartridges into guns.

Four months later, Rubio hasn't decided whether he will back or offer any legislation to limit magazine size, or if he's decided that current law is sufficient.

"I'm trying not to just find an idea but an idea that can pass," Rubio said Wednesday. "We've talked to a lot of different people involved in the industry on both sides of the debate and we're not prepared to offer any law right now because there's a lot of debate and dispute about what the right number would be and whether it would even make a difference but it's something we'll continue to explore."

Any potential bill to limit magazine size would need 60 votes in the U.S. Senate to pass.

Connecticut Sen. Chris Murphy, a Democrat who has led gun control efforts in Congress since the 2012 Sandy Hook shooting in his state, said he's "disappointed" that Rubio hasn't taken more public positions against the majority of his party on guns over the past four months, though he credited him for introducing a bill that makes it easier for law enforcement to keep guns out of the hands of people who are suspected of being threats to themselves or others.

"I certainly got a sign from Marco that he was in a little different space than he was prior to the shooting," Murphy said on Tuesday. "I'm disappointed that hasn't (happened). He did introduce red flag legislation."

Rubio's red flag bill, which he co-introduced with Florida Sen. Bill Nelson in March, has four additional cosponsors.

"That's the one I do believe can pass and we're looking for an opportunity to do it," Rubio said.

But Senate Majority Leader Mitch McConnell has not included gun-related legislation among his priorities in the U.S. Senate before the 2018 elections.

"I think his (GOP) leadership has made it clear they don't want to do anything on guns but I'm hopeful that if the moment changes, he might be willing to take a look at some commonsense measures," Murphy said.

"When I think of the handful of Republicans we can ultimately work with if we have a bill on the floor, Rubio is on that list."

Similar legislation to Rubio's red flag bill became law in Florida after the Parkland shooting, but the effort in Washington would enact red flag protections in all 50 states.

"Any Republican is swimming violently upstream if they are trying to move anti-gun violence legislation with this leadership," Murphy said. "I think we've got to live to fight another day and preserve some potential relationships. Hopefully we can work with Rubio."