Efforts in Newton to ban gun stores from the city hit a roadblock Monday after the City Council turned down proposed zoning changes to prohibit firearms retailers. But the debate over the issue will continue as councilors are expected to take up a separate ban measure in the fall. While there is widespread opposition among the city’s elected leaders against firearms businesses, debate has swirled around whether an outright ban would invite a court challenge under the Second Amendment . Late last month, the council’s Zoning & Planning Committee recommended against Newton adopting the ban through the city’s zoning code. In a 21-3 vote Monday, a majority of councilors approved the committee’s recommendation to deny the ban. Finish the story at BostonGlobe.com.