[DampRobot]

I'm sure the OP has already figured this out, but for those newer members of the forums, there's a reason why the shaft snapped at a snap ring groove. Snap ring grooves (with their sharp corners) make what's called stress risers in the shaft. The shaft's much weaker where it has a smaller diameter (at the grove itself), and the sharp corners in the groove are great places for cracks to start.

For this reason, a lot of teams avoid snap ring grooves altogether, or at least stay away from them between places on a shaft where torque is being transmitted. I'm not sure exactly what the shaft that snapped was being asked to do, but I suspect that using spacers instead of snap rings to locate components on the shaft (with snap rings near the shaft's ends or screws tapped into the shaft's ends to retain the shaft in place) would have made for a bit stronger solution.