If you are concerned about the status of firearms that are part of your father's estate as being registered or not and how to register them with ATF, you should contact a reputable firearms dealer in your area about the process for doing so and keep a record of such in your file as the estate's adminsitratrix.In order to safeguard the assets of the estate and protect you and others from any liability for unregistered firearms of filed off serial numbers, photographs all of the weapons and do an investory of them since you will need to do so anyway as part of the estate's administration.The older weapons (civil war era) should not be a concern with ATF.Good question.