  We present temperature-dependent conductivity data obtained on a sample set
of nanogranular Pt-C with finely tuned inter-grain tunnel coupling strength g.
For samples in the strong-coupling regime g > g_C, characterized by a finite
conductivity for T -> 0, we find a logarithmic behavior at elevated
temperatures and a crossover to a sqrt(T)-behavior at low temperatures over a
wide range of coupling strengths g_C = 0.25 < g <= 3. The experimental
observation for g > 1 is in very good agreement with recent theoretical
findings on ordered granular metals in three spatial dimensions. The results
indicate a validity of the predicted universal conductivity behavior that goes
beyond the immediate range of the approach used in the theoretical derivation.
