  We present the result of an extended experimental characterization of the
hexagonal intermetallic Haucke compound NpNi$_{5}$. By combining macroscopic
and shell-specific techniques, we determine the 5$f$-shell occupation number
$n_f$ close to 4 for the Np ions, together with orbital and spin components of
the ordered moment in the ferromagnetic phase below T$_C$ = 16 K ($\mu_{S}$ =
-1.88~$\mu_{B}$ and $\mu_{L}$ = 3.91~$\mu_{B}$). The apparent coexistence of
ordered and disordered phases observed in the M\"{o}ssbauer spectra is
explained in terms of slow relaxation between the components of a quasi-triplet
ground state. The ratio between the expectation value of the magnetic dipole
operator and the spin magnetic moment ($3\langle T_{z}\rangle/ \langle
S_{z}\rangle$ = +1.43) is positive and large, suggesting a localized character
of the 5$f$ electrons. The angular part of the spin-orbit coupling
($\langle\vec{\ell}\cdot\vec{s}\rangle$ = -5.55) is close to the value of -6.25
calculated for trivalent Np ions in intermediate coupling approximation. The
results are discussed against the prediction of first-principle electronic
structure calculations based on the spin-polarized local spin density
approximation plus Hubbard interaction, and of a mean field model taking into
account crystal field and exchange interactions.
