Bullets in the cabin
 

There are certain situations in Europe in which we find ourselves flying someone who is carrying ammunition (and a pistol) in the cabin, with the only stipulation that the bullets be separated from the gun (but both can still be in the passenger cabin). Do I have anything to worry about (apart from someone intentionally firing one). For example, what happens to bullets in a rapid decompression? What happens in an overhead locker fire, etc? Any research done in this field? Would any captains refuse permission?
I feel quite nervous when it happens so any info is gratefully appreciated.

I would not worry too much about it.
If weapons are allowed in an airplane's cabin, it is obviously because the people who have them, present no security risk, and are authorized to have them on board during the flight. Could be police officers as an example. Ammunition present NO danger with cabin decompression. Of course, a fire like you mention could present danger, but such fire (cabin overhead lockers) would in itself present other dangers to you and the airplane than the ammunition. Extreme situation you mention.
xxx
A pistol, in itself, even with a magazine full of bullets, presents NO danger whatsoever, provided that a bullet is NOT chambered (by "sliding" the action). Removing the magazine from the pistol is not added security. Those "cowboys" or "Dirty Harry" cops who carry a pistol with a bullet chambered with the excuse that the "safety" is ON are always dangerous. They might shoot theirselves in the foot. Same with a revolver (6 shot "wheel gun"). For these, it is better to remove the bullets from the weapon.
xxx
Do not worry either about a handgun bullet fired in the cabin by accident, piercing the fuselage. Chances are that little damage will be sustained, unless hitting certain aircraft components. Would simply be an extra air leak, like there are a few in airplanes.
xxx
I am an occasional "skeet and trap" shooter, and have, at times, taken my two guns as checked baggage, with ammunition. Other than declaring them as required, no precautions are needed for the ammunition in checked baggage.
xxx
If your name is Osama, please remove bullets from your AK-47...
And you are not welcome in my plane.
:=
Happy contrails

When a bullet is not loaded in a gun, it cannot be "fired." IF a bullet were to "cook off" in a fire, you'd already have significant other problems to worry more about. Also, the brass case would rupture first, and the lead/copper bullet would not go very far or very fast. The flying brass would be the biggest danger (since the fire is already burning, and would not be "caused" by the cook-off).

Yes, the person carrying the gun is obviously authorised, and the gun can't be loaded. I was more worried about what happens to bullets in a rapid decompression or fire. When we fight a fire, we starve it of oxygen with a BCF, but it's still hot until we get to it with water. So, in a fire I guess one of us should, while moving oxygen bottles away, also move the bullets!

Bullets and Fuselages
 

Yesterday I was talking with an Il-76 crew who work in Africa and disaster zones. They told me about a time they picked up 6 bullets in the wing and 3 around the door in the fuselage. The first they knew about it was after landing even though the wing bullets had penetrated one of the outboard fuel tanks. Obviously I knew, as a pilot, that the presence of a few bullet holes should not compromise safety unless you were REALLY unlucky, but this was the first instance I had heard of in a large commercial transport.

Overhead locker fire is likely to create bigger problems through fumes, but thi sort of thing is so extreemly rare that I can't remember reading of a single instance (and I have read AAIB and NTSB reports, monthly for the last 17 years).

RIX

When I was a young boy, father found me one day with a bonfire.
Onto the flames I had put a mortar bomb, some .303 rifle rounds and also some shotgun shells - to make a big firework. Nothing happened except that I was very sore for all the day after.