We report the results of our study of the mechanical behavior of pre-shock-loaded oxygen-free electronic (OFE) grade copper. From quasi-static data for samples of 30/~m grain size shocked to 10 GPa for 1/~s, we derive a value of the thermal component of the mechanical threshold stress (MTS) characteristic of this material that is in good agreement with values in the literature. Using the MTS model for the flow stress of OFE copper, we show that our value of the threshold stress provides an excellent description of split Hopkinson pressure bar data for a strain rate of 27(I(I s-~. We then calculate the stress-strain behavior of electromagnetically launched expanding rings of 1 l)/~m OFE copper previously shocked to 11.5 GPa for 1.6/xs, and we find excellent agreement with experimental observations, despite the large strain rate and temperature excursions characteristic of these experiments. We consider the possible influence of differences in the shock pressure and duration between the 10 and 30/~m materials on the value of the thermal component of the MTS, and we suggest that experimental scatter implied in the literature is too large to resolve any such differences. The effects of temperature and the limits of plastic flow are discussed briefly within the context of the MTS model.