  We report on the electronic and thermodynamic properties of the
antiferromagnetic metal uranium mononitride with a N\'eel temperature
$T_N\approx 53\,$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, the
magnetic contribution to the temperature dependence of the resistivity is
suppressed completely. It evolves into an almost quadratic dependence at low
temperatures indicative of a 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.
