The forced volume magnetostriction and the NMR of ferromagnetic Fe_N and ferrimagnetic Mn₄N have been measured in the ordered state. At 4.2 K the magnetization ( sigma ) per unit mass and the effective field (H_I) at the nucleus of the Fe(I) site of Fe₄N are found to change with pressure such that delta ln sigma / delta P approximately= delta ln mod H_I mod / delta P<0, while for Mn₄N delta ln sigma / delta P approximately=6 delta ln mod H_I mod / delta P>0. The result for Mn₄N is interpreted as showing that the magnitude of the small (negative) moment on the Mn(II) site decreases more rapidly under pressure than does the large Mn(I) moment. The value of delta ln mod H_I mod / delta P for Mn₄N was found to be a strong function of temperature such that delta lnT_N/ delta P approximately=5.2 Mbar^-1. An analysis of the Mn₄N NMR data suggests that the discrepancy between the calculated (spin) and measured moment at the Mn(I) site may be due to a small orbital moment at that site.