I would not be at all surprised to learn that every Fed agency, including the FDA, had a SWAT-style group. Sign of the times as the Fed becomes even more statist, and besides, the inter-departmental jealousies mandate that if Rickie gets to have guns for his people, so do I.
Hell, they've already made every local and county PD bomb squad members Special US Marshall Deputies, what's a few extra shotties in the Fed arsenal?
Besides, it gives the Feds lots more firepower, cleverly hidden within the gummint bureaucracy - harder to see. And y'all missed the fact that these have to be compatible with the ones already in stock, per the specs of their armorer.
Think on that - the IRS has an armorer.