For us it's hit or miss. But seems like Oahu is more strict. Here they always weight my ammo and even check if a few rounds are missing from the box. My trip in december the lady thought it had to also be packed inside the foam case that my gun was in. She had to check with her boss. And she was wrong.
Coming back and checking with HA, half the time they don't even weight it, they just ask that I' m under 11lbs. I've also never had to open the box in vegas HA check in either. Only a few times did I have to not open the pistol case, a verbal from me was sufficient.
So seems vegas is more lax about it than Oahu.
Based on my experience in Vegas, Honolulu and other cities, I'd characterize it more like:
Most mainland airports see more firearms being transported than Hawaii. They are therefore more comfortable and knowledgeable on the rules and procedures.
In Hawaii, I had to explain to the agent how things worked, which she had to verify with her supervisor. I was correct, and she was apologetic.
In Vegas, the agent was 100% on top of the process, and she didn't bat an eye when I declared my firearms and ammo. She had me sign my declaration, placed it inside the luggage -- NOT inside the locked Pelican case -- and put a "Special Handing" label on the bag. She was obviously accustomed to doing this, whereas the Hawaii agents appear to treat this as an "I've never done this before" encounter.
I've transported ammo to and from Hawaii. I've never been asked to weigh the ammo separately at any airport, and I can't remember being asked how much it weighed (don't make me swear to that!). I used the plastic Berry's-type ammo cases with dividers, and taped the lids closed. No problems.
I routinely fly United to use my FF miles. Maybe the difference is United vs. HA?