The Bureau of Alcohol, Tobacco, Firearms and Explosives is proposing the ban of “M855 green tip” or “SS109” rounds with certain types of metal cores. (AP Photo/Alex Brandon)

That didn't take long.

The Bureau of Alcohol, Tobacco, Firearms and Explosives said Tuesday it was backing down from a proposed ban on manufacturing and selling one of the most popular bullets used in AR-15 semiautomatic rifles.

The agency pulled the plug early, with still a week to go before the end of a one-month informal comment period on the proposed rule change that would have targeted these armor-piercing bullets. The ATF noted it had received more than 80,000 comments, and "the vast majority of the comments received to date are critical of the framework, and included issues that deserve further study."

Criticism by gun-rights groups has been withering, accusing the agency of a "back-door" attempt at gun control with the proposal it announced Feb. 16.

"The reaction?" ATF spokeswoman Danette Seward said. "All you have to do is go to our Facebook page to see the reaction."

The ATF proposal targeted 5.56mm "green tip" ammunition in SS109 and M855 cartridges. The armor-piercing bullet had been sold for years under an exemption to a 1986 law that sought to crack down on so-called cop killer bullets. Exemptions were granted if the ammunition was used mostly for sporting purposes -- hunting and target shooting -- and not in handguns. Now, the ATF sought to strip the "green tip" ammo of its exemption because of the development of AR-15 handguns that could fire the bullets.

Gun control groups applauded the move.

Gun-rights supporters responded angrily. Right-wing media accused the Obama administration of an illegal move to restrict the Second Amendment. U.S. Rep. Bob Goodlatte (R-Va.) wrote a letter co-signed by 236 members of Congress to express their "serious concern." Fifty-two senators also expressed their displeasure with the ATF's proposal.

"We have listened to the comments that people have put it, and by the sheer volume and critical nature, we've decided to put this on hold and study it further," Seward said.

Gun control supporters such as Rep. Carolyn Maloney (D-N.Y.) called the ATF's decision to back down "shameful."

"It is an outrage that in the face of terrible tragedies," Maloney said in a statement, "this country has failed to take meaningful action to protect the public from the tens of thousands of gun-related deaths every year."

Seward said the proposed "green tip" ammo ban came from the ATF's decision to review all ammo exemptions to the 1986 law. The agency had seen a recent increase in the number of "sporting purposes" exemptions requested by ammunition manufacturers. From 1986 to 2011, the agency received "very few" exemption requests, Seward said. But it has received 30 requests since then.

"We needed a clear and objective framework," Seward said.

Now, they've decided to go back to the drawing board.

Last year, the ATF successfully banned Russian-made 7N6 bullets on the grounds they were armor-piercing. Some gun-rights groups objected, but that ruling stood.

"We didn't put it out to comment," Seward noted.

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