While NJ requires a Firearm Permit to purchase or transport a firearm (shotgun or rifle, you need an additional permit per handgun), you do not need a permit to own a shotgun. So if you obtained it through other methods (such as a relative giving you one) and did not transport it off of your property, I believe you'd still be legal.
Now... the real question is, what is legality of pointing a firearm at someone in NJ on your property?
Btw, the NJ Firearms Purchasing Permit is relatively easy to get, but takes a while... you have to go to your local PD, fill out forms, get finger printed, and then wait for paperwork to be returned. Then you can use it to buy shotguns, rifles, and ammo in NJ... it also allows you to transport firearms to hunting or target shooting.