I haven't flown with a rifle in years but I assume you can still do that with a proper case, with the TSA approved locks, declare it, let them inspect it, etc. etc. If so; that's what I'd be looking at.
Last time I flew with rifles, they required you NOT to have TSA locks.
As previously mentioned, and wisely so, DO NOT USE TSA locks. Once those illiterate, ESL monkeys have visually inspected the firearm in its case and you lock it back up there is absolutely NO reason some minimum wage tarmac monkey from TSA has ANY reason or authority to open your case except to steal it.
I use a large Pelican case with rollers and pack my rifles pistols and ammunition in the case and put 4 locks on it. I’ve yet to have any trouble. I’ve found that despite my preconceived notions about the ineptitude of Shaniqua or her other ESL coworkers from TSA have no experience around firearms but they’ve always been surprisingly polite and relatively competent. The process at SeaTac is once in the terminal by the ticket counters you got to a curtained off area with a X-ray machine and a explosives detecting apparatus. They visually inspect the firearms to be sure they’re unloaded and they give you 2 copies (iirc) of their declaration form showing that they’ve inspected it. One form goes in the gun case and the other is presented to the ticketing agent or baggage handling agent and they staple it to your ticket along with the other bagge claim checks.
My buddy bought a TuffPack case that looked like a hard plastic golf club case. When ordering from Tuffpack he chose the (pick resistant NON-TSA lock. After gathering our baggage he noticed that someone in baggage or someone in TSA tried with focused determination to break into his case. It was obvious that they used a screw driver to attempt to pick the lock and when they couldn’t do that they tried to pry it open with a screwdriver. The douche-monkey that tried it was unsuccessful and only caused minor but insignificant damage to the case. That was a good learning experience because up until that point we had never had an issue with traveling with firearms.
The TuffPack isn’t cheap but compared to my Pelican it is considerably lighter. Keep in mind that there’s usually a 50# weight limit on checked bags. My Pelican case with 2 rifles, a handgun, ammunition, knife and binoculars comes in right around 50#. A little traveling scale is a great tool for saving money on excess baggage weight.
