Editing Franchi SPAS-12 (section)

==Design==
[[File:Spas12.svg|thumb|SPAS 12 with a shot diverter]]
The SPAS-12 was designed to function primarily in semi-automatic mode, with the pump-action mode used to reliably fire low-pressure ammunition such as [[tear gas]] rounds or [[less-lethal]] bean bags. The firing mode is switched by depressing the button under the fore-grip and also sliding it forwards or backwards until it clicks into position allowing the rotating sleeve to open or close the two gas ports.

The semi-automatic mode functions with a short-stroke gas piston system. When a shell is fired, the pressure makes the bolt move rearward but the bolt will stop before opening as it deploys a single top locking lug. The gas vents into the barrel and the gas port is located towards the end of the barrel. From the gas port, the gas vents downwards into the gas block where it pushes the piston rearward. Because of the presence of the magazine tube and to avoid the use of a top-mounted gas system, the gas block and the piston are annular, along with the piston spring they enclose the magazine tube. Once operated, the piston drives 2 symmetrical thin sprung operating rods located in the corners formed by the barrel and the magazine tube. As the rods push the bolt carrier rearward, it disengages the locking lug and drives the bolt rearward, allowing the system to cycle.

The SPAS-12 has a magazine cut-off feature, which prevents the magazine from releasing a new round when the action is cycled. This allows the operator to load a different type of round into the chamber without first unloading the chambered round, and the second that would otherwise subsequently be released from the magazine. 

A unique feature of the folding-stock variants is the butt hook. With the stock extended, the hook can be pushed in and turned 90 degrees to the left or right, to fit under the user's forearm. This is to enable the shotgun to be fired with one hand; e.g. while abseiling/rappelling, or from a vehicle window while driving. The hook can be released from the buttplate completely by turning 180 degrees.

SPAS-12 models feature two safeties: (i) a lever style or push button style safety, and (ii) a "quick employment safety". Lever safeties were recalled by Franchi and were replaced through the importer American Arms in the early 1990s.{{ref label|a|a}} There are two types of push-button safeties. The earliest version would release the hammer on a safe up to 1/4in. of travel when the trigger was depressed; this would cause a lockup of the action that would require the user to re-lock the bolt assembly to the rear to reset the hammer and then reload the chamber. The later version installed a [[detent]] and machined hole in the trigger group frame to prevent an action lock; the detent would prevent the hammer from engaging when the trigger was depressed and would prevent an action lock from occurring. The quick employment safety, which is on the left side of the trigger guard, disconnects the trigger when put into safe mode. The quick employment safety can be disengaged with the trigger finger when ready to fire and is intended for competition or tactical use. A third safety type, a pistol grip safety similar to the later-developed SPAS-15, is known to have been developed by Franchi for the SPAS-12, however, the pistol grip safety was not offered for sale to the general public.

A B-Square rail mount for optics was available for a short time in the 1990s as an aftermarket accessory.

The barrel of the SPAS-12 was externally threaded to accept a variety of attachments. The barrel is cylinder bored and spreads a normal shot charge to about 900mm at 40 meters.

There are four different magazine extension tubes manufactured for the SPAS-12:
# The 5-shell was designed for the 18" barrel.
# The 6-shell was designed for restriction on the standard 21.5" Sporting Purpose model.
# The 7-shell was designed for the 19{{frac|7|8}}" barrel.
# The 8-shell was designed for the 21.5 Special purpose model.

Many choke types original and aftermarket exist for the SPAS-12.<ref>{{cite web |url=http://spas12.com/ChokeAdapter.html |title=SPAS Choke Adaptor |work=Spas12.com}}</ref> A 44&nbsp;mm grenade launcher was used by France for explosive grenades capable of a range of 150 meters.<ref>{{cite magazine |url=http://www.spas-12.com/cibles-164-november-1983.html |title=Fusil Franchi SPAS12 |first=Jean |last=Huon |date=November 1983 |magazine=[[Cibles]] |language=fr |number=164 |pages=41–45 |issn=0009-6679 |via=Spas12.com |url-status=dead |archive-url=https://web.archive.org/web/20150222233915/http://www.spas-12.com/cibles-164-november-1983.html |archive-date=22 February 2015}}</ref> A factory shot diverter that spreads shot vertically or horizontally was originally included with earlier model SPAS-12s. There are many known reproduction diverters.<ref>{{cite web |url=http://spas12.com/spas12acc.htm |title=Franchi SPAS-12 Factory Accessories |work=Spas12.com}}</ref>