The vote by lawmakers in the Democratic-majority House follows mass shootings in Uvalde, Texas, and Buffalo, New York. The measure is unlikely to pass in the Senate.
The US House of Representatives has voted to raise the nationwide age limit for buying semi-automatic weapons from 18 to 21.
The measure would also ban the sale of ammunition magazines which can carry more than 15 rounds.
The move follows deadly mass shootings at a school in Uvalde, Texas, and a supermarket in Buffalo, New York.
The legislation passed the Democratic-majority House by a vote of 223-204. However, it is unlikely to be adopted in the Senate, which is split 50-50 between Democrats and Republicans.
The recent shootings have put pressure on Congress to act, with an 11-year-old survivor of the Uvalde massacre telling lawmakers about her traumatic experience on Wednesday.
