The magnetic hardening behavior of high coercivity nanograin Sm-Co magnets has been examined through a detailed investigation into their magnetic and microstructural properties. We examined the effects of various substitutions like Zr, Fe and Cu, on the magnetic behavior. Initial magnetization and remanence curves are characteristic of domain wall pinning type or single domain particle behavior. A correlation of results indicates that the reversal is controlled by the pinning of interaction domain walls at local anisotropy minima.