You can't. It will still be an AOW (Mossberg makes the PGO 500)and require a $5 tax stamp (registration)
And in Brooklyn ( where at?) I doubt it will become a reality during the current "stuff" happening
The PGO guns Mossberg makes are not AOWs.
Here's a quick run-down for those not familiar with this legal oddity.
If you have a shotgun that NEVER had a stock on it (ala Pistol-grip only) it is by legal definition not a "shotgun". Since it is not shoulder-fired.
Thus it can not be classified as a short barreled shotgun, since it was never a shotgun to begin with.
It also can not be classified as an AOW as long as the overall length stays over 26". The prerequisite to be an AOW is it must be concealable (which the ATF defines as under 26")
So if you have a shotgun that is PGO from the factory you can cut the barrel down as short as you want, as long a you keep the whole thing over 26" and never attach a stock to it. It will simply be classified as a "firearm" Just like a stripped AR lower.
With a Mossberg 500, if you install one of those birdshead grips on it you can cut the barrel down to 14.5" (flush with the mag tube) and still remain over 26" OAL.
As far as I can see neither NYS or City seem to have any additional laws regarding this issue. As such it's as legal as any other pump gun. I know, AMAZING. I figured there would be some kind of law broken by this thing. But NOOOPE.
I know Mossberg 500s come with PGOs from the factory. But I prefer the Maverick's safety position so would really rather do it with one of those if possible.
Edit: Link http://shockwavetechnologies.com/site/?page_id=88