A possible alternative etymology: I believe the answer is tied up in the name 'Quick-silver Bullets' (note the hyphen, it is a deliberate addition). A careless reader assumes that hydrargyrum, mercury, is meant, but if one looks up the entry for the bullets we find that they contain the blood of the hunter. Now it is a common folk belief that evil things can only be killed by a silver bullet (cf. Bonnie Dundee, alias Bluidy Clavers -- a general during the Jacobite rising in 1689, said by the Covenanters to have sold his soul to the Devil and so could only fall by a silver bullet) and the graphics of the bullet seem to suggest that they are of silver. So far, so good, but why 'Quick'silver? I believe that the answer lies in the archaic meaning of the word 'quick', which is 'alive'. The Anglican Prayer Book alludes to 'the quick and the dead' in the Creed. Old English 'cwic' meant 'living' first and foremost. Thus, as they are made, if you allow my contention, of silver mingled with the hunter's blood, they truly are made of quick or living silver, silver into which blood has been enfused. I would be interested to know the Japanese name and the reasons for the chosen translation.
Heavy Bullets is a PC game played by Ross and Barry on Steam Train. Episodes Impish By Nature, Knife Party!