After the WW2 Schweizerishe Industrie-Gesellshaft company, also known as SIG, decided to produce an all-new submachine gun, better suited for modern tactics and significantly less expensive that relatively unsuccessful SIG MKMO submachine guns of pre-WW2 period. The first such weapon appeared in 1948. Known as SIG MP-48, it was relatively simple and compact design, which made good use of modern precision steel casting techniques. Despite of its merits, sales of MP-48 were relatively weak, with the only one major customer being the Chile. During late fifties, when SIG switched over to special model numbers rather than year of introduction model designation, a final SIG submachine gun was brought to the market. Known as SIG MP-310 (the 3xx model indexes were reserved for submachine guns, while 2xx indexes were reserved for pistols and 5xx - for assault rifles), this weapon was also sold internationally in limited numbers. The key difference between MP-48 and MP-310 was that the latter used precision cast polymer stock instead of the wooden stock of the predecessor. Otherwise both guns were quite similar. Production of the SIG MP-310 continued until about 1972, and in limited numbers. Few were sold to South America, and some were purchased by various Swiss police organizations.
SIG MP-310 submachine gun is simple blowback operated weapon that fires from open bolt. Fire mode selection is made by the pull of the trigger, short pull producing single shots and long pull producing automatic fire. No manual safety was provided on the weapon, as the folding magazine housing was considered sufficient for this purpose. When magazine was folded forward, to lie horizontally below the barrel, the gun was completely safe and compact. A push on the magazine housing lock button, located on the left side of the gun, released the magazine and permitted it to fall under its own weight to vertical (ready to fire) position, where it was locked by same button-operated catch. Sights were adjustable for range between 50 and 200 meters (rotary drum-type rear sight with 4 notches). Stock was made from plastic integral with pistol grip, with telescoped buttstock made of steel wire.