Originally Posted by JimN
The lower is the only part with a serial number, AFAIK. anyone can buy the rest of the parts and assemble one if they have the lower but the lower is, or will probably be, regulated. If AR-type guns are outlawed and people are willing to go to great lengths to get one/many, this is one way to go about it.
Gangs and other criminals don't buy guns for a lifetime, they only need them once, really. If it lasts that long, they got their money's worth, IMO.
But an 80% aluminum lower has no serial number and can be sent through the postal service too. There are YouTube videos with guys making AR lowers out of aluminum in their garage too. If I was looking for illegal weapons - I'd want one that at least I knew was going to fire when I needed it - if you read about the guys making plastic lowers, they have lots of failures and their "successes" get them a couple hundred shots before they break or wear out. I get your point though - it is feasible to do so - just not very practical given the other better options out there.