Hmmm, I didn't see that. You might want to try calling the public Range 14 at Fort Dix. They are really cheap ($50/year) but the days and hours of operation are limited. They do have a 300 yd range, but I don't know about shooting .50's. Give them a call if you are interested, 609-562-4676.
I really don't think they would have a problem, since there are full-auto .50's going off constantly not far away, during maneuvers...
If ye love wealth better than liberty, the tranquillity of servitude better than the animating contest of freedom, - go from us in peace. We ask not your counsels or arms. Crouch down and lick the hands which feed you. May your chains sit lightly upon you, and may posterity forget that ye were our countrymen!
1 August 1776