You must declare firearms in checked baggage when you check them.
Bring the hard case that has at least two lock hasps with the unloaded firearms inside to the airline check-in counter. Ammunition must be in factory cartons or cases designed to hold individual ammunition cartridges in their own compartment (no loose rounds, and no rounds in magazines or clips). Check your airline for their policy on ammunition quantity limits (it varies). Bring four non-TSA locks. They must be non-TSA locks because you must sign a affadavit that you alone have the key or combination and that no one else does and you cannot truthfully sign such knowing anyone else has TSA keys. Tell the airline agent you have firearms to declare (it's preferred you not use the word "gun") and that you have the locks. They'll have you sign the form declaring the firearms unloaded state and regarding the locks. They will instruct you from there.
At some airports, the airline agent will escort you to TSA with your case. Remind the TSA person you have the locks or if the airline had you put them on, remind TSA that you can remove them if necessary. This saves them from cutting them off. In some cases, they will just cut them off, and you will need the other two locks you brought with you. Yes, it can be that inane. It is the federal Government. If you don't want to be stopped from flying, bring four locks. Two locks might not be strictly required, but you do not want to get in an argument with someone who is convinced they remember something about locks on each end of a long gun cases or whether your snubnosed revolver is actually a long gun. Two locks per case avoids the argument. You would not believe how stupid people can be. I've heard them argue about whether guns had to be in individual hard cases or one hard case was enough for multiple guns. If you can avoid any arguments, its worth it because if someone decides to dig-in, your clock is running and you will be late for your flight while they will just go off shift and it's another day.
At some airports, the airline will have you lock the case with your affadavit inside and they deliver it to TSA. In this case, TSA x-rays the case and they'll do whatever they have to do or contact you if needed. It's more likely to happen this way at very small airports. Most of the time, expect to accompany your case to the airline and TSA.
If you've checked a bag with a firearm, expect to have to pick it up at the Baggage Service Office, and not off the carousel.
Also, you consent to the search when you check bags. It is not an illegal violation of your 4th amendment rights if you waive those rights and you do indeed do so when you check bags or consent to the search at the TSA checkpoint.
I don't think TSA should focus on guns, but on fire and explosive risks which do include lithium batteries besides bombs. Handguns should be allowed carry-on because a handgun cannot take down the entire plane. Some pilots and Sky Marshals are armed, but why not arm random passengers at their will? Terrorists and other would-be-hijackers with careful planning such as those that perpetrated 9/11 can easily identify pilots and sky marshals that carry and take them out by surprise. They cannot anticipate which passengers are armed and willing to resist and only firearms give otherwise weaker people the ability to overcome a stronger hijacker. The bottom line is an airline passenger compartment should not be a gun-free zone.
Pretty amazing how much energy that little thing generates and for how long. Imagine it going off at 30,000 ft. 