Congressional Democrats are demanding the ATF use "existing authority" to ban a popular bullet. The move comes just days after the Bureau of Alcohol, Tobacco, Firearms and Explosives backed off a proposal to ban the M855 green-tip cartridges, one of the most popular bullets used in AR-15 rifles.

The public comment period for the proposed ban closes Monday but in the face of overwhelming public opposition the ATF announced last week that they were going back to the drawing board.

Not good enough for Democrats. They sent a letter, obtained by The Hill, which says the ATF needs to act to keep, "dangerous ammunition out of our communities."

"We hope that the Bureau will swiftly review comments on the proposed framework and issue a revised proposal that will address the danger posed by handguns that fire 5.56mm and other rifle ammunition," Democrats write in the letter.

The letter expresses disappointment with the ATF decision.