kmm16-
The DOJ advice about serial #s and local PDs is laughable. Law enforcement has no relationship to serial# issues other than checking them if something perceived as a possibly stolen gun comes their way. That DOJ verbal info is worth the paper it's written on and the desk clerk who told you of this must be smoking crack.
Just add your own unique identification on receiver: "Bob Smith #1".
However - again! - please steer clear of homebuilt AR/AK receivers.
While there are DOJ letters that indicate a homebuilt "off-list" AR/AK receiver would be legal, those are not binding opinion letters.
There is, I feel, some chance that - if it ever entered court - one of the 58 DAs could somehow say that Harrott protections don't apply to homebuilt receivers as that is so impracticable that the decision couldn't cover those. The receiver could thus possibly fall back under Kasler, leaving you in a world of hurt. I don't know if this is a bigger or smaller risk but a gun attorney I spoke to nodded in agreement when I mentioned my feelings about this. So only get off-list AR/AK receivers that are in general commerce. [By contrast, despite the warnings from DOJ about 58 DA opinions and off-list lowers, we have a very secure, clear, easy-to-read court decision protecting the legality of such items.]
And there is zero chance a homebuilt AR/AK receiver would be able to get listed as an AW by DOJ.
At this time there is no rational legal or financial reason to have a homebuilt receiver for AR/AK type guns.
Bill Wiese
San Jose