IMO not really. For example some countries (eg Germany) have different rules for which parts of guns are serialized and regulated. So it's possible to get a bar

IMO not really. For example some countries (eg Germany) have different rules for which parts of guns are serialized and regulated. So it's possible to get a barrel for a legal rifle and replace the lower receiver with fully automatic HK416 parts, which are available over the counter without any licensing or other restrictions.