I was reading a book recently called payback by andy McNab in the book Fergus Watts makes a bomb out of c4 and a paint can but he fills the paint can with nuts, boolts and other small metal objects. Fergus (in the book) states that the nuts & bolts will be able to cut through any armoured car like a hot knife through butter.

It's a shrapnel bomb. This type of explosion is really meant to kill exposed personel, rather than people in hard targets such as armoured vehicles.

The exploding C4 will send the nuts and bolts flying out in a spherical pattern tearing through people like hundreds of little bullets. This is a very effective tool used to inflict maximum casulties.

Now can this shrapnel penetrate an armoured vehicle? Most armoured vehicles are designed with this type of threat in mind and would withstand up to a certain threshold. The vurnable areas are likely the windows and various seams and joints, but I suspect his claim to "cut through like a hot knife", is exaggerated somewhat.

Usually it's just a paint can full of petrol, and various metal that explodes. I suppose C4 could pack more of a punch, as petrol explosions are more for show, as hollywood proves.

However I do agree, it'd have to be very sharp and going awfully fast to piece a metal vehicle. Even then it'd have to be at a weak point, otherwise it'd just leave a mark at best.

Define 'armoured car'? If we are talking hardened military vehicle, then no, the C4 paintcan will not work - the can is basically just a claymore mine, with even less detonation energy than a Mills Bomb-style grenade, (the 'power', or burn speed of the explosive is largely irrelevant in this instance, the containment vessel is what increases the pressure and magnifies the detonation - and a paintcan isn't very effective,) and military vehicles are designed to easily withstand this, even lightly armoured stuff, like Scorpion ARV's.

If, as I suspect, we are talking 'bulletproof' limousines and their like, the levels of protection offered by these vehicles varies considerably. The U.S. President's vehicle, at one extreme, actually enjoys a higher level of blast and impact protection than many military vehicles. At the other extreme, a mercedes E-class ordered from the factory with standard 'Guard-Safe' protection will only really stop handgun and carbine bullets, and not that many of those. High-velocity rifle bullets or shrapnel will penetrate these easily, especially with multiple, localised hits at close range.

McNab is an exiting writer, but like many ex-forces writers, sometimes gets a bit carried away with all the exitement. Plus which, it is quite a while since he's been in uniform - there are many more effective explosives around than C4 - C4 is so last year, don't you know!