An effort in Congress, backed enthusiastically by anti-gun groups, aims to ban most centerfire autoloaders on the market. 

While past "assault weapon bans" use a combination of naming specific models and their cosmetic features to target semi-automatic firearms, the proposed new Gas-Operated Semi-Automatic Firearms Exclusion, or GOSAFE, Act, instead targets pistols, rifles, and shotguns that use any sort of spent propellant gases to cycle the action during the reload process. The result is that the only guns not affected would be autoloaders with low-capacity fixed magazines, revolvers, single/double shot firearms, and those with a manual bolt, lever, or pump action. 

"For years, I have said that rather than using the appearance of these guns to restrict them, we should instead focus on how these weapons actually work and the features that make them especially dangerous," said U.S. Sen. Angus King, a Maine independent who caucuses with the Democrats. King introduced the GOSAFE Act in the Senate along with co-sponsors Mark Kelly (D-Ariz.), Martin Heinrich (D-NM), and Michael Bennet (D-Colo.).

While the 20-page bill includes exemptions for firearms chambered in .22 rimfire or less, as well as shotguns and rifles with a "permanently fixed magazine of 10 rounds or less" and handguns "with a permanently fixed magazine of 15 rounds or less," most other guns are on the cutting block. The language includes specific bans on everything else that uses a short or long-stroke gas piston, direct impingement action, blowback action, or recoil-operated system, and accepts some sort of detachable magazine. 

“The legislation introduced by Senators King and Heinrich is openly defiant of the rights protected by the U.S. Constitution" -- Larry Keane, NSSF.

The bill would establish a definition for a "Large Capacity Ammunition Feeding Device" which includes a traditional box-style detachable magazine as well as any "belt, drum, feed strip, helical feeding device, or similar device" capable of holding more than 10 rounds of ammunition. 

While guns and magazines in circulation when the bill becomes law would be grandfathered, they could not be transferred outside of a limited pool of the owner's close family members. 

Penalties for violating the law would carry a fine of up to $5,000 and 12 months in federal prison. Committing a crime with one of the banned types present would add 10 years to a possible sentence. 

The bill also has sweeping provisions that would establish a fee-based "licensed manufacturer application process" through the Attorney General for all future semi-automatic firearm design approval, create a taxpayer-funded voluntary "buy-back" program for outlawed guns and magazines, and prevent "unlawful firearm self-assembly and manufacturing."

The GOSAFE Act has the early endorsement of all the major (and several minor) gun control organizations including Brady, Everytown, and Giffords. Of note, Giffords was co-founded by bill co-sponsor, Sen. Kelly.

However, pro-Second Amendment and firearms industry groups are strongly against the measure. 

“The legislation introduced by Senators King and Heinrich is openly defiant of the rights protected by the U.S. Constitution,” said Lawrence G. Keane, the National Shooting Sports Foundation's Senior Vice President and General Counsel. "There is no path forward for legislation of this nature that would deprive law-abiding citizens the ability to lawfully possess the firearm of their choosing and the full spectrum of their Second Amendment rights."