A "firework" (a shot in the dark) in New Years Eve. Since there are Latin letters GB, the name might be Georg Ferdinand Bruns/Bruhns born 29.6.1816, died 13.7.1893 (maybe?), active in Riga. The assayer is Vladimir Alekseyevich Galkin 1842-1844, but I guess you already new that..
Getting a confirmation might be difficult. Sometimes you just have to rely on your intuition when there are no other alternatives. Happy New Year to you too Q