Extensive wave shape data are presented for various (effectively) unconfined explosives over wide ranges of diameterd, lengthL, density &rgr;1, and physical conditions. Observed wave fronts were invariably spherical segments with radii of curvatureRincreasing at first directly withL(R=L), but eventually becoming steady at a constant valueRm/dbetween 0.5 and 4 depending on the charge diameter primarily through the ratioa0/d(a0=reaction zone length). At the critical diameter of propagation (largea0/d)Rm/dapproached 0.5, and at large diameter (smalla0/d) it approached or leveled off at the upper limit of about four. The upper limit (Rm/d∼4) is apparently a restriction imposed by the fundamental nature of detonation of solid explosives with free boundaries.