Police searched a property in Blackwood
A 24-year-old man from south Wales has been charged with possessing a firearm and also explosive substances.
Darren Tinklin, 24, of Blackwood, Caerphilly, had been questioned by the Metropolitan Police after his arrest under the Terrorism Act on Friday.
He will face seven charges when he appears before Westminster Magistrates on Wednesday, said a force spokesman.
Two other men, aged 24 and 41, who were arrested at the same time, have been released without charge.
The Met said the charges include possessing an improvised muzzle loading firearm, and making an explosive substance, called Black Powder.
Mr Tinklin was also charged with possessing explosive substances - potassium nitrate, charcoal and a "pipe bomb"' at a property in Waunllwyn Crescent.
He also faces a charge of possessing a document containing information "of a kind likely to be useful to a person committing or preparing an act of terrorism".
Gwent Police initially arrested three men in Blackwood on suspicion of drugs offences last Wednesday.
The Metropolitan Police Service Counter Terrorism Command was called in the next day after further inquiries.