The chemical composition of the Orion star-forming region. III. C, N,
  Ne, Mg and Fe abundances in B-type stars revisited
  Early B-type stars are invaluable indicators for elemental abundances of
their birth environments. In contrast to the surrounding neutral interstellar
matter (ISM) and HII regions their chemical composition is unaffected by
depletion onto dust grains and by the derivation of different abundances from
recombination and collisional lines. In combination with ISM or nebular
gas-phase abundances they facilitate the dust-phase composition to be
constrained. Precise abundances of C, N, Mg, Ne, Fe in early B-type stars in
the Orion star-forming region are determined in order to: a) review previous
determinations using a self-consistent quantitative spectral analysis based on
modern stellar atmospheres and recently updated model atoms, b) complement
results found in Paper I for oxygen and silicon, c) establish an accurate and
reliable set of stellar metal abundances to constrain the dust-phase
composition of the Orion HII region in Paper II of the series. A detailed,
self-consistent spectroscopic study of a sample of 13 narrow-lined B0V-B2V
stars in Ori OB1 is performed. High-quality spectra obtained with FIES@NOT are
analysed using a non-LTE method and line-profile fitting techniques, validating
the approach by comparison with results obtained in Paper I using
line-blanketed non-LTE model atmospheres and a curve-of-growth analysis. The
two independent analysis strategies give consistent results for basic stellar
parameters and abundances of oxygen and silicon. The extended analysis to C, N,
Mg, Ne, and Fe finds a high degree of chemical homogeneity, with the
1sigma-scatter adopting values of 0.03--0.07 dex around the mean for the
various elements. Present-day abundances from B-type stars in Ori OB1 are
compatible at similar precision with cosmic abundance standard values as
recently established from early-type stars in the solar neighbourhood and also
with the Sun. (abridged)
