The intertwined "EF" on the individual tubes is the preliminary mark for Ferlach. The "NP" sub "F" is the nitro proof at Ferlach and possibly final proofmark by later rules? The 2 headed eagle was either the mark of a final examination or a 3rd proof if required and should have a "1" on the breastplate. "216.68" would be the 216th example thru the Ferlach proofhouse in 1968. I would guess the "15087" to be the serial number. "12/70" is the bore & chamber length. And Boehler Blitz is of course the steel type and I think it was a rung below Antit.
Kind Regards,
Raimey
rse
