One of my friends is leaving soon for a two week hunt in NZ and was informed yesterday that Air NZ would not carry his firearms because he was connecting from a different air carrier. Supposedly this took effect May 28, 2015 but I had no problems in June 2015 with my rifle being transferred from another carrier (non code share) so maybe they are now enforcing their regs...to me the simple fix would be to claim and recheck baggage before boarding Air NZ flights, I bet that would work. Anyone else had this problem?

In May of 15' I reclaimed from my JFK to LAX leg and rechecked for the Air NZ part of the trip as there was not a code share for the flights.

No issue with Air NZ with that, and no issue carrying back Tahr cape/skull/horns in checked bags and clearing USF&W (added maybe an hour). Wish I could do that on every trip!

Karl,
At USA check-in is your friend able to check baggage all the way through to Auckland / Christchurch, NZ ? If he can that should resolve the issue. I am not intimately familiar with Air NZ policy on firearms carriage but they are one of the firearms friendliest airlines around so I suspect the info your friend received is incorrect.
Personally, in October 2015, with firearms I flew Boise / San Fran ( on United / code share ), San Fran / Auckland ( Air NZ ). At Boise I checked luggage right through to Auckland with absolutely no problem. In fact the airlines folks could not have been more helpful.

where does he change airlines , and who is he with before and after the change?

Have always found ANZ very good when flying with firearms.