Casting to sub classes.cs

public class BaseMessage
{
    Guid moduleReference;

    public Guid ModuleReference
    {
        get { return moduleReference; }
        set { moduleReference = value; }
    }
    int processReference;

    public int ProcessReference
    {
        get { return processReference; }
        set { processReference = value; }
    }
    string screenCode;

    public string ScreenCode
    {
        get { return screenCode; }
        set { screenCode = value; }
    }

    char recordStatus;

    public char RecordStatus
    {
        get { return recordStatus; }
        set { recordStatus = value; }
    }
    bool isActive;

    public bool IsActive
    {
        get { return isActive; }
        set { isActive = value; }
    }
    DateTime createdDate;

    public DateTime CreatedDate
    {
        get { return createdDate; }
        set { createdDate = value; }
    }
    DateTime lastUpdatedDate;

    public DateTime LastUpdatedDate
    {
        get { return lastUpdatedDate; }
        set { lastUpdatedDate = value; }
    }
    string lastUpdatedUsercode;

    public string LastUpdatedUsercode
    {
        get { return lastUpdatedUsercode; }
        set { lastUpdatedUsercode = value; }
    }

    #region "Casting to sub classes"

    /// <summary>
    /// Converting BaseMessage to DomesticPaymentMessage
    /// </summary>
    /// <returns></returns>
    public virtual DomesticPaymentMessage ToDomesticPaymentMessage() 
    {
        DomesticPaymentMessage msg = new DomesticPaymentMessage();

        FillField(msg);
        return msg;
    }

    public virtual DomesticPaymentMessage ToDomesticPaymentMessage(DomesticPaymentMessage msg)
    {
        FillField(msg);
        return msg;
    }

    /// <summary>
    /// Converting BaseMessage to ForeignPaymentMessage
    /// </summary>
    /// <returns></returns>
    public virtual ForeignPaymentMessage ToForeignPaymentMessage() 
    {
        ForeignPaymentMessage msg = new ForeignPaymentMessage();

        FillField(msg);
        return msg;
    }

    public virtual ForeignPaymentMessage ToForeignPaymentMessage(ForeignPaymentMessage msg)
    {
        FillField(msg);
        return msg;
    }

    private void FillField(BaseMessage msg) 
    {
        msg.ModuleReference = this.ModuleReference;
        msg.ProcessReference = this.ProcessReference;
        msg.ScreenCode = String.IsNullOrEmpty(this.ScreenCode) ? "" : this.ScreenCode;
        msg.RecordStatus = this.RecordStatus;
        msg.IsActive = this.IsActive;
        msg.RecordStatus = this.RecordStatus;
        msg.LastUpdatedUsercode = this.lastUpdatedUsercode;
        msg.LastUpdatedDate = this.LastUpdatedDate;
        msg.CreatedDate = this.CreatedDate;
    }

    #endregion
}

public class DomesticPaymentMessage
        :BaseMessage
{

}

public class ForeignPaymentMessage
    :BaseMessage
{
    int accountType;

    public int AccountType
    {
        get { return accountType; }
        set { accountType = value; }
    }
    int accountBranchCode;

    public int AccountBranchCode
    {
        get { return accountBranchCode; }
        set { accountBranchCode = value; }
    }
    int accountNumber;

    public int AccountNumber
    {
        get { return accountNumber; }
        set { accountNumber = value; }
    }
    int accountSuffix;

    public int AccountSuffix
    {
        get { return accountSuffix; }
        set { accountSuffix = value; }
    }

    public override ForeignPaymentMessage ToForeignPaymentMessage()
    {   
        return base.ToForeignPaymentMessage(this);
    }
}