The permit for the temporary export and reimport is still ongoing. I will provide this too. But the airline guy already told me he needs to see something with UN0012 printed on it. I just hope that @BourbonTrail 's document mentioning only the 1.4S will suffice.This means they want you to prove that these are small arms cartridges, do you have any approval from the authorities permitting you to take the firearm and ammo abroad? Perhaps send them a copy of that along with the picture of CIP proof marks and calibre from the ammo box.
I wrote RWS for their own version of the safety data sheet, with the same mention.