Protesters were giving away 1,200 30-round magazines. The legislation would ban high-capacity magazines and rapid-fire devices known as bump stocks, in addition to raising the legal age. It would also expand background checks for private gun sales.
People who own high-capacity magazines before the law takes effect can keep the high-capacity magazines.
Gun rights advocates also were accepting donations for a fund to challenge the Vermont legislation.
Republican Gov. Phil Scott is expected to sign the bill.