depending on a single attorney general's opinion on whether or not bump stocks (b/s) is legal or not in hawaii may not be best. a future attorney general might reverse the current opinion.
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to remove all doubt, the legislature will have to pass a law specifically banning b/s.  
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a.t.f. allowed the sale of bump stocks after determining that b/s are not firearms in themselves, but merely a part that does not alter the internal firing mechanism. the agency ruled they only have jurisdiction over firearms not parts so the b/s were allowed into the market as a part. 
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obama was president when the a.t.f. decided they had no jurisdiction over the b/s part. but, you can bet obama would have issued an executive order banning the b/s if he knew about it or saw it in action. 
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a.t.f., alone, owns this b/s decision.
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a.t.f. should issue a ban on the b/s immediately. otherwise, obama's 57 u.s. state legislatures will have to wait until their next legislative sessions to ban the b/s.
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