The pre-bans and many post-bans were imported under the Heckler & Koch name. The pre-bans allow the legal installation of the full length mag tube in the pistol grip models. If you have the full stock model, you can add the full length mag tube regardless of manufacture date. Some people have said that the current Benellis have less robust parts than the older ones imported under the HK name. I cannot agree or disagree as I have yet to compare the two side by side.
