Can I purchase long guns on Oahu with my permit issued from the Big Island?   Thanks!

Technically, no, because permits are issued by the chief of police of the county where the gun is to be acquired.

But Hawaii gun laws are so strange that this may not be enforced, or may be extended to other counties. Best bet is to call both Honolulu PD firearms and Hawaii county firearms for an answer. My guess is no, because by strange, i mean requiring an FFL for in state transfers of firearms and ammunition between islands. I can't even find this law on the books...

Or requiring a permit application and waiting period for the return of firearms seized by HPD, but already owned by you.

How strange.

I bought 2 pistols on the BI with my Maui permit. I don't see what the problem would be. You're going to register it with your county, not island you bought it on.

i mean requiring an FFL for in state transfers of firearms and ammunition between islands.

You do not need a FFL to transfer firearms intra state you can ship direct to the buyer.

FFL's and ammo

Honolulu is a very strange place, in this respect. I heard about the intra-state FFL requirement from the guy that came to teach the instructor course. He is from Hilo and has a FFL and was required to send something (i cant remember if it was a gun or ammo, or both) to a Honolulu FFL. I personally haven't tried, so i do not know. I would recommend calling the firearms departments from both counties.