Quoted:
You remove the "preban" upper and replace it with a "postban" upper, or alter the "preban" upper to "postban" configuration. As the BATF said, possession of the rifle is not prohibited even though the receiver is marked, "Resticted, Law Enforcement Use Only."
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Anyone who possesses a lower that is marked, "Resticted, Law Enforcement Use Only" is asking for trouble one day or another, without some documentation stating otherwise.
The "Restricted..." markings will cause someone from BATF to ask if they excise tax has been paid, as it may have been a department buy, are you legally able to own the firearm, etc.
You might be 100% in the right to possess, but do you want to spend a couple thousand dollars proving it when you could have bought a complete lower for $200-300? A private citizen in possession of such a firearm who is pulled over and the firearm is found, someone at range notices the markings and has Deputy Joe come over to see how you got a LEO only firearm, and the list goes on.
Be smart about what you are doing.
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