This work is aimed at experimentally exploring the effects of minor compositional variables upon the combustion behavior of composite solid propellants. More specifically, it is intended to determine the influence, if any, of ingredients that improve the mechanical properties upon the oscillatory combustion characteristics. Tests are carried out in the familiar Crawford bomb, a low-pressure L*burner, and a high-pressure T-burner. Two families of propellants are investigated; each family consists of two propellants with a minor compositional variation between them. In the family that shows a decreasing (steady state) pressure index (n) with increasing pressures, all of the combustion characteristics are found to be very similar although the mechanical properties are widely different. In the other family, which shows an increasing n with increasing pressures, unmistakable differences are found between the two propellants in the low-pressure L*instability behavior (along with the differences in the mechanical properties), while the other combustion characteristics are almost identical. The results are interpreted to be consistent with a theory that highlights the importance of condensed phase heat-transfer effects.