(a) “Ability to accept a detachable magazine” means with respect to a semiautomatic shotgun, it does not have a fixed magazine.

(b) “Action” means the working mechanism of a semiautomatic firearm, which is the combination of the receiver or frame and breech bolt together with the other parts of the mechanism by which a firearm is loaded, fired, and unloaded.

(c) “Barrel” means the tube, usually metal and cylindrical, through which a projectile or shot charge is fired. Barrels may have a rifled or smooth bore.

(d) “Barrel length” means the length of the barrel measured as follows: Without consideration of any extensions or protrusions rearward of the closed bolt or breech-face the approved procedure for measuring barrel length is to measure from the closed bolt (or breech-face) to the furthermost end of the barrel or permanently attached muzzle device. Permanent methods of attachment include full-fusion gas or electric steel-seam welding, high-temperature (1100°F) silver soldering, or blind pinning with the pin head welded over. Barrels are measured by inserting a dowel rod into the barrel until the rod stops against the closed bolt or breech-face. The rod is then marked at the furthermost end of the barrel or permanently attached muzzle device, withdrawn from the barrel, and measured.

(e) “Bullet” means the projectile expelled from a gun. It is not synonymous with a cartridge. Bullets can be of many materials, shapes, weights, and constructions such as solid lead, lead with a jacket of harder metal, round-nosed, flat-nosed, hollow-pointed, et cetera.

(f) “Bullet-button” means a product requiring a tool to remove an ammunition feeding device or magazine by depressing a recessed button or lever shielded by a magazine lock. A bullet-button equipped fully functional semiautomatic firearm does not meet the fixed magazine definition under Penal Code section 30515(b).

(g) “Bore” means the interior of a firearm's barrel excluding the chamber.

(h) “Caliber” means the nominal diameter of a projectile of a rifled firearm or the diameter between lands in a rifled barrel. In the United States, caliber is usually expressed in hundreds of an inch; in Great Britain in thousandths of an inch; in Europe and elsewhere in millimeters.

(i) “Cartridge” means a complete round of ammunition that consists of a primer, a case, propellant powder and one or more projectiles.

(j) “Centerfire” means a cartridge with its primer located in the center of the base of the case.

(k) “Contained in” means that the magazine cannot be released from the firearm while the action is assembled. For AR-15 style firearms this means the magazine cannot be released from the firearm while the upper receiver and lower receiver are joined together.

(l) “Department” means the California Department of Justice.

(m) “Detachable magazine” means any ammunition feeding device that can be removed readily from the firearm without disassembly of the firearm action or use of a tool. A bullet or ammunition cartridge is considered a tool. An ammunition feeding device includes any belted or linked ammunition, but does not include clips, en bloc clips, or stripper clips that load cartridges into the magazine.

An AR-15 style firearm that has a bullet-button style magazine release with a magnet left on the bullet-button constitutes a detachable magazine. An AR-15 style firearm lacking a magazine catch assembly (magazine catch, magazine catch spring and magazine release button) constitutes a detachable magazine. An AK-47 style firearm lacking a magazine catch assembly (magazine catch, spring and rivet/pin) constitutes a detachable magazine.

(n) “Disassembly of the firearm action” means the fire control assembly is detached from the action in such a way that the action has been interrupted and will not function. For example, disassembling the action on a two part receiver, like that on an AR-15 style firearm, would require the rear take down pin to be removed, the upper receiver lifted upwards and away from the lower receiver using the front pivot pin as the fulcrum, before the magazine may be removed.

(o) “Featureless” means a semiautomatic firearm (rifle, pistol, or shotgun) lacking the characteristics associated with that weapon, as listed in Penal Code section 30515.

(p) “Fixed magazine” means an ammunition feeding device contained in, or permanently attached to, a firearm in such a manner that the device cannot be removed without disassembly of the firearm action.

(q) “Flare launcher” means a device used to launch signal flares.

(r) “Flash suppressor” means any device attached to the end of the barrel, that is designed, intended, or functions to perceptibly reduce or redirect muzzle flash from the shooter's field of vision. A hybrid device that has either advertised flash suppressing properties or functionally has flash suppressing properties would be deemed a flash suppressor. A device labeled or identified by its manufacturer as a flash hider would be deemed a flash suppressor.

(s) “FMBUS” means a Firearm Manufactured By Unlicensed Subject.

(t) “Forward pistol grip” means a grip that allows for a pistol style grasp forward of the trigger.

(u) “Frame” means the receiver of a pistol.

(v) “Grenade launcher” means a device capable of launching a grenade.

(w) “Permanently attached to” means the magazine is welded, epoxied, or riveted into the magazine well. A firearm with a magazine housed in a sealed magazine well and then welded, epoxied, or riveted into the sealed magazine well meets the definition of “permanently attached to”.

(x) “Overall length of less than 30 inches” with respect to a centerfire rifle means the rifle has been measured in the shortest possible configuration that the weapon will function/fire and the measurement is less than 30 inches. Folding and telescoping stocks shall be collapsed prior to measurement. The approved method for measuring the length of the rifle is to measure the firearm from the end of the barrel, or permanently attached muzzle device, if so equipped, to that part of the stock that is furthest from the end of the barrel, or permanently attached muzzle device. (Prior to taking a measurement the owner must also check any muzzle devices for how they are attached to the barrel.)

(y) “Pistol” means any device designed to be used as a weapon, from which a projectile is expelled by the force of any explosion, or other form of combustion, and that has a barrel less than 16 inches in length. This definition includes AR-15 style pistols with pistol buffer tubes attached. Pistol buffer tubes typically have smooth metal with no guide on the bottom for rifle stocks to be attached, and they sometimes have a foam pad on the end of the tube farthest from the receiver.

(z) “Pistol grip that protrudes conspicuously beneath the action of the weapon” means a grip that allows for a pistol style grasp in which the web of the trigger hand (between the thumb and index finger) can be placed beneath or below the top of the exposed portion of the trigger while firing. This definition includes pistol grips on bullpup firearm designs.

(aa) “Receiver” means the basic unit of a firearm which houses the firing and breech mechanisms and to which the barrel and stock are assembled.

(bb) “Receiver, lower” means the lower part of a two part receiver.

(cc) “Receiver, unfinished” means a precursor part to a firearm that is not yet legally a firearm. Unfinished receivers may be found in various levels of completion. As more finishing work is completed the precursor part gradually becomes a firearm. Some just have the shape of an AR-15 lower receiver for example, but are solid metal. Some have been worked on and the magazine well has been machined open. Firearms Manufactured by Unlicensed Subjects (FMBUS) began as unfinished receivers.

(dd) “Receiver, upper” means the top portion of a two part receiver.

(ee) “Rifle” means a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of the explosive in a fixed cartridge to fire only a single projectile through a rifled bore for each single pull of the trigger.

(ff) “Rimfire” means a rimmed or flanged cartridge with the priming mixture located in the rim of the case.

(gg) “Second handgrip” means a grip that allows the shooter to grip the pistol with their non-trigger hand. The second hand grip often has a grip texture to assist the shooter in weapon control.

(hh) “Semiautomatic” means a firearm functionally able to fire a single cartridge, eject the empty case, and reload the chamber each time the trigger is pulled and released. Further, certain necessary mechanical parts that will allow a firearm to function in a semiautomatic nature must be present for a weapon to be deemed semiautomatic. A weapon clearly designed to be semiautomatic but lacking a firing pin, bolt carrier, gas tube, or some other crucial part of the firearm is not semiautomatic for purposes of Penal Code sections 30515, 30600, 30605(a), and 30900.

(ii) “Shotgun with a revolving cylinder” means a shotgun that holds its ammunition in a cylinder that acts as a chamber much like a revolver. To meet this definition the shotgun's cylinder must mechanically revolve or rotate each time the weapon is fired. A cylinder that must be manually rotated by the shooter does not qualify as a revolving cylinder.

(jj) “Shroud” means a heat shield that is attached to, or partially or completely encircles the barrel, allowing the shooter to fire the weapon with one hand and grasp the firearm over the barrel with the other hand without burning the shooter's hand. A slide that encloses the barrel is not a shroud.

(kk) “Spigot” means a muzzle device on some firearms that are intended to fire grenades. The spigot is what the grenade is attached to prior to the launching of a grenade.

(ll) “Stock” means the part of a rifle, carbine, or shotgun to which the receiver is attached and which provides a means for holding the weapon to the shoulder. A stock may be fixed, folding, or telescoping.

(mm) “Stock, fixed” means a stock that does not move, fold, or telescope.

(nn) “Stock, folding” means a stock which is hinged in some fashion to the receiver to allow the stock to be folded next to the receiver to reduce the overall length of the firearm. This definition includes under folding and over folding stocks.

(oo) “Stock, telescoping” means a stock which is shortened or lengthened by allowing one section to telescope into another portion. On AR-15 style firearms, the buffer tube or receiver extension acts as the fixed part of the stock on which the telescoping butt stock slides or telescopes.

(pp) “Those weapons with an ammunition feeding device that can be readily removed from the firearm with the use of a tool” includes functional semiautomatic rifles, pistols, and shotguns with bullet-button style magazine releases. These weapons do not have a fixed magazine.

(qq) “Thumbhole stock” means a stock with a hole that allows the thumb of the trigger hand to penetrate into or through the stock while firing.

(rr) “Threaded barrel, capable of accepting a flash suppressor, forward handgrip, or silencer” means a threaded barrel able to accept a flash suppressor, forward handgrip, or silencer, and includes a threaded barrel with any one of those features already mounted on it. Some firearms have “lugs” in lieu of threads on the end of the barrel. These lugs are used to attach some versions of silencers. For purposes of this definition a lugged barrel is the same as a threaded barrel.