Senate Democratic leaders expect a gun bill to move to the Senate floor that includes most of the proposals backed by President Barack Obama, with the notable exception of a ban on military-style, semiautomatic weapons, a top aide to Majority Leader Harry Reid of Nevada said.

The bill would likely seek to limit the capacity of ammunition magazines; expand background checks to include sales at gun shows and other private transactions; and require better record keeping to keep guns out of the hands of those with mental illnesses. It would also try to curb gun sales in states with more relaxed gun laws to buyers in states with stricter laws.

The details provide the first snapshot of how Senate Democrats plan to move forward on major gun legislation in coming weeks.

But the strategy outline also reflects a growing sense within Democratic ranks that some of the president's most ambitious goals—particularly the call for new bans on certain types of military-style guns often described as assault weapons—may be unrealistic, the Reid aide said.

The goal is to get the bill to the Senate floor next month, at which point lawmakers could then seek to amend the legislation by adding a ban on certain semiautomatic weapons or other provisions, the aide said.