For several years, we have been studying the thermodynamics of the metamagnetic phase transition in CoMnSi and substituted versions. Our motivation has been that the metamagnetic transition, between a non-collinear antiferromagnetic (AFM) state and a higher temperature ferromagnetic (FM) state, can be reversibly and adiabatically invoked near room temperature by a magnetic field. The material is therefore a candidate room temperature magnetic refrigerant - employing the internal transfer of entropy between degrees of freedom on application of the field. We have recently found a large difference between the electronic DoS in the AFM and FM states, and a giant magnetostriction associated with the transition between them. We plan to study the temperature and magnetic field dependence of lattice parameters and magnetic structure in CoMnSi-based materials around the metamagnetic transition.