57Fe Mössbauer studies were carried out on the phases HoErFe17-xGax (x=0-7) and HoErFe17-xGaxC (x=0, 1, and 2) at 25 K and room temperature. The weighted average hyperfine field at room temperature is found to increase initially for low Ga content and then decreases for phases with higher Ga concentration. The hyperfine fields at Fe sites follow the sequence 4f(6c)>6g(9d)>12j(18f)>12k(18h), which is determined mostly by the number of Fe and R nearest neighbors. The variation of the weighted average hyperfine field with temperature is found to obey T2 behavior, suggesting the presence of single-particle excitations. Insertion of carbon at interstitial sites is found to increase the individual site hyperfine fields and hence an increase in the weighted average hyperfine field. The 12j and 12k sites of Fe show significant increase in isomer shift compared to other Fe sites.