I fly fairly regularly out of Logan w/firearms. It’s much less troublesome than you may be imagining.
You’re required to use non-TSA locks on the gun cases and you will keep the keys on you after checking them in.
No need to label the locks, when you arrive at the counter (must use Full Service check in line) just hand the person your Drivers Lic, and calmly declare that you need to check a couple firearms. They typically will not even blink an eye at it, it’s much more common than you may think and they’re used to it.
They will fill out a small tag, maybe ask you to show them that the cases are locked properly and ask if they’re unloaded and that any ammo is packed accordingly and separate from the firearms themselves. You will then write your name, address and phone number on the back of the firearms tag, and either place it on top of the case or they tape it to the case for you. If TSA needs you they then have your phone number to call you and meet you for any issues. This has only happened once to me because one of my ammo boxes was damaged/unusable on my trip so I stuffed like 50 rds on ammo in a sock, TSA had issue with this and called my cell, the TSA guy came and found me and explained that he’d need to confiscate the ammo as it can’t travel that way, meh, I was ok with that and understood and the guy was pretty cool about the whole thing.
Ironically flying out of Logan with a firearm(s) is much easier than a lot of other airports I’ve gone thru. Expect that when flying back to Logan at the end of your trip, their checks will be different. You will do the same, check in, declare firearm, and fill out the tag to put inside your bag or on rifle case.
They then may make you wait for a TSA agent to come to the check in line and then follow them to one of their back rooms, where they will them open your bag and go thru all of your clothes, gun boxes and ammo boxes. They will swab everything for explosive residue and run the swabs thru their machine in the back room looking for anything that stands out other than gun powder residue.
It’s a little frustrating and takes extra time before you can even get into the security line, so be prepared to always arrive and give yourself an extra 30mins than originally expected.
I’ve never been detained for longer than that, and never, knock on wood, had any firearms stolen while traveling.
Just be casual about it, it’s a daily occurrence for airports everywhere. Not a big deal at all. Have fun!
ETA: When you land don’t waste time doing anything except going directly to luggage pick up. Sometimes they’ll be right on the conveyer belt and sometimes they’ll be automatically brought to the office for lost/special items and you’ll need to show ID to pick it up. Quick and easy and I prefer when they do this as their are thieves that show up at airports just to try and steal a couple bags and walk out like they own them.