A spokesman for BlackRock said the company doesn't discuss its voting plans prior to a shareholder meeting.
In another shareholder proposal this year, nuns asked Dick's Sporting Goods, a major gun seller in the U.S., to re-evaluate its sales of military-style assault weapons to civilians, among other requests.
On Wednesday, Dicks' CEO Edward Stack, announced the company will stop selling assault rifles and restrict sales of other firearms to those 21 and older. He said he had been impressed by the student protests in Florida.
Dicks had legally sold a shotgun to the 19-year-old who has confessed to the shooting in the Florida high school, though that particular gun was not used. "Clearly this indicates on so many levels that the systems in place are not effective to protect our kids and our citizens," Stack said in a statement. "We believe it's time to do something about it."
On Wednesday, Mercy Investments confirmed to CNBC it had withdrawn the proposal with the retailer earlier this month after talking with executives about their concerns.
Last year a climate change proposal on the ballot at Exxon led by Sister Nora Nash, director of corporate responsibility for the Sisters of St. Francis in Philadelphia, garnered 62 percent support. It was a stunning reversal from prior efforts by the religious group that failed to win a majority vote.
The support of fund giant Vanguard as well as BlackRock pushed the proposal over the goal line.
Normally, religious groups have strict rules that forbid them from owning shares of companies that make tobacco and guns or engage in activities that aren't in keeping with their values. But this time, the nuns bought gun maker shares so they could take their case directly to the companies, Byron said.
The gun makers haven't filed their proxy materials for shareholders yet, so it is unknown whether they will ask the Securities and Exchange Commission for permission to keep the proposals off their ballots. Walmart successfully excluded a proposal by Trinity Church of Wall Street in 2015 but ultimately did stop selling certain types of rifles and high-capacity weapons in its stores.
Calls to Sturm Ruger and American Outdoor weren't returned.
Sturm Ruger seems likely to tell shareholders to vote against her proposal, Byron said. In 2002, the gun maker also recommended a "no" vote.
"Like many companies, we receive proposals from well-meaning stockholders. Many are commendable, and their objectives are often aligned with our values," Sturm Ruger said in its 2002 proxy. "We share the goal of firearms safety raised by this proposal, but we believe that there are appropriate safety practices and procedures in place."
Less than 5 percent of Sturm Ruger shareholders voted in favor of the proposal.