I know if that if they bring a firearm that they currently own from a different state, they have 5-days to get it registered with HPD. Can I sell it to someone who does not have a Hawaii ID, but is a part-time resident here? Since I've been told that local gun shops can only sell to Hawaii residence. I'm not asking if they can own it without registering it, I'm asking if they can buy it from me, and leave the pistol in Hawaii so it's available for their use when they are here.
You seem to understand the difference between acquiring and registering a firearm. That's good.
Simple: Have him go get the permit from HPD. If he can pass the permit application process, then you have nothing to worry about regarding residency.
Once the pistol is transferred, he needs to register it in HI no matter where he intends to keep it.
As stated, he needs to decide where to store it when he's gone. A gun box only he has access to in a friend's house, or secured in a place he rents or owns year round, should be fine.
He can also have an FFL store it. I don't know if they charge much for that. Depending on if he's military or LE and which FFL, he might find someone willing to store it for free if it's a short period each time. Many gun shop owners are very accommodating to their regular customers. Make sure he buys lots of ammo, targets and gear from the store if they help him on the storage!
