Mechanical alloying is used to produce a metallic precursor for MgB2 formation. Micron-scale mixing of magnesium and boron powders allows the MgB2 formation reaction to proceed at as low as 450 °C, with high-quality material formed in an hour at 600 °C. These low reaction temperatures allow the reaction to be performed in situ in a copper sheath. Critical current densities, calculated from a full critical-state simulation of magnetization hysteresis loops, are up to 7×105 A/cm2 at 13.6 K and 1×105 A/cm2 at 30 K, in zero applied field. © 2003 American Institute of Physics.