  We report on the electronic and thermodynamic properties of the
antiferromagnetic metal uranium mononitride with a N\'eel temperature
$T_\mathrm{N}\approx 53\,$K. The fabrication of microstructures from single
crystals enables us to study the low-temperature metamagnetic transition at
approximately $58\,$T by high-precision magnetotransport, Hall-effect and
magnetic-torque measurements. We confirm the evolution of the high-field
transition from a broad and complex behavior to a sharp first-order-like step,
associated with a spin-flop at low temperature. In the high-field state, a
quadratic temperature dependence of the in-plane resistivity indicates its
metallic character. Our detailed investigation of the Hall effect provides
evidence for a prominent Fermi-surface reconstruction as the system is pushed
into the high-field state.
