Copper is widely used as additive in low alloyed sintered steels since it promotes liquid phase formation below the common sintering temperatures. However, the Cu swelling effect upon melting leads to some limited dimensional accuracy of the sintered parts. A newly developed Cu-based master alloy (MA) is proposed to diminish this problem. Its design is based on an improved wetting capability of the liquid over an iron substrate which enables excellent distribution of the alloying elements with lower impact on the dimensions of the parts. This work assesses the dimensional and sintering behavior of steels modified with this MA. The sintering process is first analyzed through DTA and dilatometry experiments carried out on plain iron and Cr-prealloyed steel compacts with 0.7 wt.%C and 2 wt.%MA under both inert and reducing atmospheres (Ar, H2, 90%N2-10%H2). Sintering of steels with varying contents of MA (1-4 wt.%) and carbon (0.25-0.7 wt.%) is also performed at 1120°C under 95%N2-5%H2 in a continuous belt furnace. The results reveal an improved dimensional control of the parts while maintaining or even improving the structural properties of the steel.