  We analyse the leading logarithmic corrections to the $a^2$ scaling of
lattice artefacts in QCD, following the seminal work of Balog, Niedermayer and
Weisz in the O(n) non-linear sigma model. Restricting our attention to
contributions from the action, the leading logarithmic corrections can be
determined by the anomalous dimensions of a minimal on-shell basis of
mass-dimension 6 operators. We present results for the SU(N) pure gauge theory.
In this theory the logarithmic corrections reduce the cutoff effects. These
computations are the first step towards a study of full lattice QCD at
O($a^2$), which is in progress.
