SSG is "Swan Shot", in English size 0.30" or 7.62mm diameter, the American equivalent is #1 Buck, Australian SSG is slightly smaller, 0.27" or 7.23mm.
I assume the device pictured is a flare pistol, and possibly made of plastic?
(Over here it would be classed as a "Prohibited Weapon" under s.5 of the Act - pistol or short (!!!) barrelled shotgun.)
Anyone even _thinking_ of producing a flare pistol that will chamber and fire 12ga shotgun cartridges should be locked up for their own (and everyone else's) safety. IMAO, of course.
Chris.