when it comes to AR platform are any legal to use in the field? 

Yes, on private property only.  NJ restricts rifle hunting to certain game with only certain sized projectiles.  See the fall hunting guide for specifics  From the NJDFGW Guide

 

A valid rifle permit must be in possession while hunting with a modern rifle. Rifles for small game hunting are allowed using limited types of .22 caliber rimfire ammo and are legal only for taking woodchuck (ammo restrictions, page 56), raccoon and opossum with hounds (.22 shorts only) plus coyote and fox (ammo restrictions, page 54). NO rifle woodchuck hunting on wildlife management areas or state parks, forests and recreation areas. Small game hunting with centerfire rifles is limited to not larger than .25 caliber for coyote and fox (see page 54) and .25 caliber or larger for woodchuck (see page 56). See also Firearms and Missiles, page 24. A modern rifle magazine need not be pinned (plugged), but may be loaded with no more than three cartridges. Rife permit holders of all ages may hunt with all rifle types as allowed by New Jersey laws. See chart on page 56 for details on small caliber rifle ammunition legal for hunting woodchucks and page 54 for the special permit coyote/fox season.

Yes, it is legal for fox and coyote.

Woodchucks on private land only.

 

Call F&W directly, the numbers are on the back of your license, for questions that you may have after reading pg. 54-57 of the digest. Always best to hear it from them in order to remove any doubt or confusion.

Thank you for your expertise guys!