I'd guess the cipher or interlaced characters on the water-table & the flats to be BV, which may be modelled after the British? The chamber info is inverted with the C atop the bore unlike the Belgian and Birmingham stamps. The other mark of Crown over FB/B, encircled or not, seems to mimic the Belgian Crown over encircled & spangled ELB. So maybe some mechanic from an Eastern Block country that sourced components from Liege, w/ the NON POUR BALLE stamp? Haven't a clue on the FP?

Cheers,

Raimey
rse