Yep. Just like when someone goes out of a tobacco shop and has a "water pipe" or a pipe with a big bowl in the middle. 99% of the time they aren't used for tobacco. As a matter of fact it is ILLEGAL to call a "water pipe" a "bong" in Nebraska. Also can't talk about lagalization. You'll get kicked out of the shop. Similar. Call something illegal in all other cases a different name and you're fine. If you are building your own firearm that can't be traced, you are probably not going to use it for something legal. Just watch In The Line Of Fire. Or look at how people are making firearms from 3d printers. They think they are getting away, but, modern forensics will catch up. Amazing about how a little mud, or a seed, or little fibers from clothes can trace you to the firearm. I could see a machinist doing one just for fun, but everyone else is probably up to something.

It's still legal is my point. Hell, I know of people that hunt deer with an AR-15. But you need a min of a 62 grain projectile (most are 55), and you can't have more than 5 rds.

Or maybe you want to be a competition speed shooter.

@TheGreatShadow If you know people who hunt with an AR-15 I have a bridge to sell you....or you know some seriously ill people.