I haven't seen the movie you're talking about, but you could almost be describing this thing by Knight's Armament:
Built on a GP-100, firing a silenced 30-calibre cartridge, and able to be disassembled and carried in a briefcase. The Tsarist Russians also built stocked versions of their 1895 Nagant revolver for use by border-guards, but they didn't have the range necessary, so they ended up dropping them.