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Bump fire stocks, gunstocks that are specially designed to make bump firing easier, are of varying legality in the United States. Sales are illegal in some states, and in several other states the regulatory status is unclear. The Department of Justice on March 23, 2018 announced a plan to change the regulatory status of bump stocks. The proposed change would classify bump stocks as "machine guns" and effectively ban the devices in the United States under existing federal law. If the rule becomes final, people would be required to destroy or surrender existing devices.
On April 17, 2018, Slide Fire Solutions, the sole holder of the bump stock patent, announced that it would cease production of bump stocks as of May 20, though they did not state whether this was a temporary or permanent measure. It has temporarily suspended production before.
The bump firing process involves bracing the firearm with the non-trigger hand, releasing the grip on the firing hand (leaving the trigger finger in its normal position in front of the trigger), pushing the firearm forward in order to apply pressure on the trigger from the finger, and keeping the trigger finger stationary. During a shot, the firearm will recoil ("bump" back) and the trigger will reset as it normally does; then, the non-trigger hand pulls the firearm away from the body and back to the original position, pressing the trigger against the stationary finger again, thereby firing another round when the trigger is pushed back.
Normally, a rifle is held securely and firmly against the shoulder, but the loose shoulder hold that creates the rattle to rapidly depress the trigger affects accuracy in a way that is not encountered with firearms that are designed for select-fire.
A similar method can be employed with semi-automatic pistols, in which one hand holds the grip, two fingers are placed in the trigger well, and then the grip hand shoves the firearm forward while the trigger fingers remain stationary. With revolvers, rapid fire can be achieved by using two trigger fingers firing offset.
All these techniques greatly degrade the accuracy of the firearm. The techniques trade accurate, aimed fire for an increase in the firearm's rate of fire. The inaccuracy renders the practice uncommon for precision target shooting, but is increasingly popular for applications where volume of fire is favored over accuracy. None of these techniques fire more than one round with a single trigger pull; rather they compensate for biomechanical limitations associated with how fast a finger can repetitively pull the trigger.
With bump firing, it is common to use all the rounds in the firearm's magazine, but it becomes easy to create a stoppage as the cycling of all semiautomatic firearms requires the bolt to move against the stationary firearm (low-mass semiautomatic pistols suffer from the same problem due to "limp wristing"). The bolt must complete the stroke against the spring, and that doesn't happen if both the bolt and spring are moving rearward. Non-bump fire rifles can suffer the same failure from fouling or for undercharged ammunition. Blanks also can cause these failures. Additionally, it is possible that if a gun is bump-fired too fast, then the hammer will be released before the bolt closes. This will either cause the hammer to "ride" the bolt carrier without firing the chambered round or cause the firearm to slamfire.
Bump fire stocks
Bump fire stocks are gunstocks that are specially designed to make bump firing easier, which allows semi-automatic firearms to somewhat mimic the firing speed of fully automatic firearms. Bump fire stocks can be placed on a few common weapon platforms such as the AR or AK families. They can achieve rates of fire between 400 to 800 rounds per minute depending on the gun. As of 2018[update], bump fire stocks in the United States may sell for around $100 and up, with prices increasing due to potential regulation.
Regulatory status in the United States
The ATF ruled in 2010 that bump stocks were not a firearm subject to regulation and allowed their sale as an unregulated firearm part. In the 2017 Las Vegas shooting, twelve bump fire stock devices were found at the scene. The National Rifle Association stated on 5 October 2017, "Devices designed to allow semi-automatic rifles to function like fully-automatic rifles should be subject to additional regulations", and called on regulators to "immediately review whether these devices comply with federal law". The 2017 shooting generated bipartisan interest in regulating bump stocks. On 4 October 2017 senator Dianne Feinstein introduced a bill to ban bump stocks, but as of November 3, 2017, no Congressional action had resulted. Instead, President Trump instructed the ATF to issue regulations to treat bump stocks as machineguns. A notice of proposed rulemaking was issued by the ATF on March 29, 2018, and opened for public comments.
On November 3, 2017, Massachusetts became the first state to enact a ban on both sale and possession of bump stocks after the Las Vegas shooting. Sale of bump stocks had been illegal in California since 1990; legal status is unclear in Connecticut, Michigan, Minnesota, Puerto Rico, and Washington, D.C.
Bump stocks were banned in New York with the passage of the NY SAFE Act in 2013. In his final day as governor in January 2018, New Jersey Governor Chris Christie signed legislation making the gun accessory illegal in New Jersey.
On February 20, 2018, President Trump proposed regulatory bans on devices, including bump stocks, that "turn weapons into machine guns." The Department of Justice on March 23, 2018 announced a plan to change the regulatory status of bump stocks. The proposed change would classify bump stocks as "machine guns" and effectively ban the devices in the United States under existing federal law. If the rule becomes final, people would be required to destroy or surrender existing devices. The proposal has a 90-day comment period.
On March 9, 2018, after the 2018 Stoneman Douglas High School shooting, the state of Florida enacted SB 7026, which, among other things, banned bump stocks. Some parts of the bill took effect immediately, but the portion banning bump stocks takes effect October 1, 2018. Vermont passed a similar law in 2018. Hawaii, Maryland, and Washington followed suit.
Patent infringement suit
Slide Fire Solutions filed suit against Bump Fire Systems for infringement of its patents on bump stock designs in 2014. The suit alleged that Bump Fire Systems infringed eight US Patents, for example, United States Patent No. 6,101,918 entitled "Method And Apparatus for Accelerating the Cyclic Firing Rate of a Semi-Automatic Firearm" and United States Patent No. 8,127,658 entitled "Method of Shooting a Semi-Automatic Firearm". The suit was settled in 2016, resulting in Bump Fire Systems ceasing manufacture of the product in contention.
Survivors of the October 1, 2017 mass shooting that took place in Las Vegas, Nevada have sued bump stock patent holder Slide Fire Solutions, claiming the company was negligent and that they deliberately attempted to evade U.S. laws regulating automatic weapons: "this horrific assault would not and could not have occurred, with a conventional handgun, rifle, or shotgun, of the sort used by law-abiding responsible gun owners for hunting or self defense." 
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