When Democratic lawmakers introduce a new assault weapons ban later today they will display some of the guns they hope to make illegal, Democratic aides say. Included will be a Bushmaster rifle, one of the weapons police say was used to kill 20 children and six adults in Newtown, Conn. last month.

The D.C. police have signed off on the weapons' display, so the lawmakers won't face the same problems NBC News' David Gregory encountered last month when he held up an illegal gun clip on television. 

Longtime gun control advocates Sen. Dianne Feinstein (Calif.) and Rep. Carolyn McCarthy (N.Y.) will introduce the legislation this morning, along with a slate of Democratic co-sponsors. Both lawmakers have pushed for the ban before in part because of their personal histories with gun violence.

The bill is a far-reaching attempt to rein in the use of such weapons by prohibiting the sale, transfer and manufacturing of more than 100 specific weapons, including certain semiautomatic rifles, handguns and shotguns that can hold detachable magazines or hold more than 10 rounds of ammunition.

Ed O'Keefe contributed to this report.