http://www.arsenal-bg.com/history.htm
From 1977 till 1989 the factory was known in Bulgaria and abroad as "F.Engels" Machine Building Plant. The machinery fleet is continually improved and modernized thus enlarging the possibilities for a wider scale of production. Simultaneously grew the number and the qualification of the specialists. All that was a premise for perfecting the licenced production, design and serial production of new products:
1971-72 - 9x18 mm pistol cartridges;
1971-73 - 7,62 mm "Kalashnikov" machine gun PK;
1972-74 - 9 mm "Makarov" pistol;
1976-78 - 7,62 mm "Kalashnikov" tank machine gun PKT;
1983 - 23 mm anti-aircraft system ZU-23-2;
1984-86 - 5,45 mm "Kalashnikov" assault rifle AK-74, AKS-74;
1985-87 - 5,45x39,5mm cartridges;
1986-87 - 122 mm howitzer etc.