Gun thread of SRS

So according to the ATF a stripped lower is just a part even though it has a serial and is registered as a firearm. So by their definition we don’t have a firearm until it’s a fully functional rifle. Therefore wouldn’t you technically just be buying a part out of state. Either way the problem is the state police taking liberty with the law and saying any lower is illegal even though it is possible to assemble a semi or bolt rifle on a AR platform and comply with this B.S. law.