How do you unlock all the weapons in army of two the 40th day

To unlock all of the weapons you need to play through the campaign and make different combinations of co-op choices to get the weapons
EX; you can take the weapons from the storage locker and get the m416 but by making a negative choice you can't get the G18c from the doctor so you have to play through a couple of times to get them all

other weapons can be found in packages throughout the levels ATTENTION: at the end of the game, jonah has a bomb detonater, and he says that if u shoot him, the whole city blows us, its a fraud, he jus doesnt want u to shoot him, but do it anyways