The assault weapons ban bill authored by U.S. Sen. Dianne Feinstein, D-Calif., is being assailed by critics who say the legislation exempts 2,200 guns, including firearms that could be used in future mass shootings.

Feinstein was the architect of the 1994 assault weapons ban that expired in 2004. Momentum has been building to reinstate the ban since the Newton, Conn., shootings at Sandy Hook Elementary School in December that killed 20 children and six adult staff members.

One of the 2,200 guns exempted from the new bill includes a model of the Ruger .223 caliber Mini-14, a firearm used in the 1986 FBI Miami shootout. Two FBI special agents were killed in the incident by bank robbers Jeff Dove and Ben Grogan.

FBI agent John Hanlon, who participated in the shootout, told the Associated Press that the exemption is “a joke.”

The version of the Ruger .223 caliber Mini-14 that is banned under Feinstein’s bill has a collapsible stock that makes the gun more portable. But Hanlon argues that both versions are just as deadly, because they’re capable of firing dozens of rounds without reloading.

“I can’t imagine what the difference is,” Hanlon told the AP.

The list of 2,220 exempted guns includes weapons used for hunting and sporting. Any gun owners who possess any of the 157 guns banned under the bill don’t have to turn in their firearms; the legislation only bans the models from being manufactured in the future. Feinstein said banned guns include military-style firearms and semi-automatic weapons.

Critics of the assault weapons ban bill complained that the list of exempted guns appears arbitrary in some cases.

“There’s no logic to it,” Greg Danas, president of Massachusetts-based G&G Firearms Experts, told the AP. “What kind of effect is it going to have?”

Lawrence Keane, senior vice present of the Newtown, Conn.-based National Shooting Sports Foundation, agreed.

“The bill demonstrates a shocking ignorance of the product they are purporting to regulate,” he said, according to the AP. “I have no idea how they arrived at this list. It would seem to be random, bordering on throwing darts at a dart board.”

Those against the bill point to the M-1 Carbine being exempted for the arbitrary nature of the exemptions. The M-1 is an assault rifle developed for the military and is banned from being imported into the country.

Feinstein wrote to the AP, saying experts disagreed on whether to ban or exempt the M-1.

“It has been used in multiple police shootings and was originally used by U.S. soldiers on the battlefield,” she wrote to the wire service. “On the other hand, it comes in models that would not meet the military characteristics test.” She said she decided to limit banned weapons to those that met the definition outlined in the bill.

However, Feinstein’s bill does have wide support, with Mayors Against Illegal Guns, a coalition organized by New York City Mayor Michael Bloomberg, urging Congress to take action on an assault weapons ban bill.

"Military-style assault weapons and high-capacity ammunition magazines have been at the center of some of our country’s deadliest mass shootings," the coalition wrote in a letter to congressional leaders. "Just since July, we have watched in horror as they have been used to gun down moviegoers in an Aurora theater, Sikh worshippers in an Oak Creek temple and even young children in a Newtown elementary school. In order to prevent the next rampage and help save American lives, our nation needs clear and enforceable legislation that will take these weapons and magazines off our streets."