"Bullet Bobbins" are shuttle's...... the Bullet is the shuttle, te long round thing the thread winds around is the bobbin,
VS is and abbreviation of "Vibrating Shuttle" the "standard" VS machine swings the shuttle front to back ( front being where you sit, back being the side towards wall .... Transverse machine the Shuttle goes left to right ( end where the hand wheel is being right, and end where the needle is being left )