There are two key steps to carrying out a dam break analysis.
1. Produce the dam break hydrograph
2. Use a hydraulic model to model the flow downstream of the dam
HEC-RAS will not produce the dam break hydrograph. Modelling of the failure of earth embankment dams is not a straightforward task. We have produced software that can be used to model dam breaks and produce the dam break hydrograph see: https://www.dambreach.org/
With regards to HEC-RAS, you can use this software to model the mud and debris flow (i.e. non-Newtonian flow) downstream of a dam failure. This video gives a good introduction to using the HEC-RAS software to model mud and debris flow: https://www.youtube.com/watch?v=HCk30TkNcnA From our experience, HEC-RAS does have some limitations with regards to the number of cells you can have in a model but it's pretty good for a free piece of software.
The U.S. Army Corps of Engineers uses HEC-RAS to simulate dam and levee failures for applications throughout the world. It is free to download and distributed with excellent documentation. Check out training materials detailing the use of HEC-RAS within dam safety studies here: https://www.hec.usace.army.mil/training/materials.aspx#HYDROLOGY_AND_HYDRAULICS_FOR_DAM_SAFETY_STUDIES. Within this class, we typically devote 2.5 days to hydraulic modeling topics including estimating breach parameters, setting up a dam failure simulation, diagnosing/fixing model stability problems, and visualizing results. Let me know if you have any additional questions.