Create a new profile and call it 'Shooterman' ... This'll give you every single level to play in... (PS: i worked it out from the game manual... in the death match screen shots you see the name Shooterman... and so i thought i'd give it a go... and what do you know it worked :) thats what happens when the camel has too much time on his hands... like now really)

In Killzone (multiplayer or single), when you have the shotgun and you are aiming at an enemy, press the primary and secondary fire at the same time. This will fire three shells at one time, capable of killing an enemy from around medium distance. Be warned, however. After doing this twice, you have two shells left, providing less power. This runs your ammo down pretty fast, so try and use it in places like Park Terminal, where you can usually go short distances for more shotgun ammo.