the crossed fronds (?) on the barrel flats are the in-house quality ratings of the tubes....examples seen here are 3 crossed fronds, another step up with 4 crossed fronds, and the mf set with 5 crossed fronds (not precisely the same stamp as the prior examples - but likely conveying the same, or similar meanings).
the mf set is also marked acier hercule tempe, as indicates a heat tempering process and is seen on upper grade guns from mf - also note that set of barrels is from a 450 double rifle...not a shotgun.
best regards,
tom
