NY still pretty much use the old Assault weapons ban verbatim, where a gun suddenly transforms into an evil assault weapon when it "has two or more of the following".
NY's AWB last I knew said
Semi-automatic shotguns with two or more of the following: |
* Folding or telescoping stock
* Pistol grip
* Fixed capacity of more than 5 rounds
* Detachable magazine
They key word being "semi automatic" which a Mossy 500 is not. So you should be fine.
However I know that several retailers are out there who don't want to get anywhere near involved in the various states laws will just simply blanket not sell certain products to certain states.
I live in Maryland where we have a handgun roster (only approved guns on the list can be sold in Maryland). The list is non the less huge and pretty encompassing and gets updated several times a year as new guns come out and it is rare that you find a gun that is not on the list. But even still there are several sellers on gun broker for instance that refuse to sell handguns to Maryland buyers even though the gun is on the approved list because they don't want to deal with the issue. Whether its seller laziness, ignorance, or they are worried too much about liability whatever.
Perhaps that is the same thing with the seller that refused to sell you the folding stock.
I would call up the local sherrif's office or state police and ask to speak with their firearms section to be sure though but as I read it, the restrictions only apply to semi auto shotguns.