I have an 80% lower and I am going to start a build. Recently I was at a gun shop and they told me it is illegal to build from an 80% because it’s considered “manufacturing”. I’ve always been told it was legal to build for yourself but not for others and it couldn’t be sold without a serial number. I’ve seen 80% lowers at other gun shops so I think they’re just trying to get me to buy a stripped lower. Can anybody give me a little more info on the laws regarding 80% lowers and building the gun?