We have designed, constructed, and operated a 70-period microwiggler for free electrons lasers (FELs). The device is a pulsed ferromagnetic-core electromagnet with a period of 8.8 mm, which generates an on-axis peak magnetic field of 4.5 kG. The pulses, of 0.5 ms duration, are generated at a rate of 0.5 Hz. Each field peak is independently tunable. We employed a novel tuning regimen to reduce the rms spread in the peak amplitudes to 0.08%, the lowest value thus far attained in a sub-cm-period periodic magnetic field.