Agent Callen take cover behind a Dozer bucket when Chambers is firing at him. The bucket takes multiple hits from Chamber's 9mm handgun leaving several large holes visible. The Bucket on a Dozer is made of very thick heavy gauge steel and would not sustain any noticeable damage from a small pistol cartridge. Anything less than a large caliber high powered rifle with AP rounds would do nothing but scratch such heavy metal.
Near the end of the episode, a stray bullet detonates a van full of RDX. Neither impact nor fire will blow up RDX. It takes a detonator.
Military units do not transport weapons and ammunition together. All NATO countries have military regulations which require separate vehicles for weapons, ammunition, and the weapons' firing pins or bolts. These rules are in place to prevent exactly the type of ambush and weapons theft depicted in this episode.
When the Callen is taken hostage, the man with the AK has the safety on as he is pointing it. It is very difficult to take the safety off on an underfolder AK with the stock folded, so his rifle was basically useless.