STEPControl_Reader reader;
reader.ReadFile("c:/tmp/cylinder.stp");
//reader.ReadFile("c:/tmp/quader.stp");
reader.TransferRoots();

Handle(StepData_StepModel) stepModel = reader.StepModel();
Interface_EntityIterator entities = stepModel->Entities();

for (entities.Start(); entities.More(); entities.Next()) {

    Handle(Standard_Transient) value = entities.Value();

    if (value->IsKind("StepShape_ManifoldSolidBrep")) {
        Handle(StepShape_ManifoldSolidBrep) downCast = Handle(StepShape_ManifoldSolidBrep)::DownCast(value);
        Handle(Transfer_TransientProcess) pr = reader.WS()->MapReader();
    
        //Crashes with cylinder.stp on writing
        //Works with quader.stp on writing
        StepToTopoDS_Builder builder(downCast, pr);
        TopoDS_Shape value2 = builder.Value();
        
        //Works - but gets shape of root not of specific entity
        //TopoDS_Shape value2 = reader.OneShape();

        STEPControl_Writer writer;
        writer.Transfer(value2, STEPControl_ManifoldSolidBrep);
        writer.Write("C:/tmp/output.stp");

    }
}