The phrase "Fire Away", meaning "Ask me questions", appears to be a metaphor stemming from an old military term involving discharging firearms (source). However, "Away" is generally a directional term, yet in the phrase "Fire away" it seems to mean "at will" or "with abandon". How did it get such an unusual meaning? Was this a sarcastic instruction perhaps?
I read "fire away" almost the same way that I would "bombs away", as an order to "release" the projectile, not a suggestion for where they can put their projectiles. A longer form might have been "let the fire be away" or "let the fire be on its way". This has the feeling of something that could be an actual order as opposed to an order to whiff, which militaries tend not to do for reasons involving accidental murdering.
Say on; say what you have to say. The allusion to firing a gun; as, You are primed up to the muzzle with something you want to say; fire away and discharge your thoughts.
“Foster, I have something I want you and Miss Caryll to understand.” “Fire away!” exclaimed Foster. — Watson: The Web of a Spider, chap. xv.
Fire away, Flanagan.
A taunt to a boaster. A man threatening you, says he will do this, that, and the other; you reply, “Fire away, Flanagan.” Cromwell marched against a castle defended by Flanagan, who threatened to open his cannon on the Parliamentarians unless they withdrew. Cromwell wrote on the corner of the missive sent to him, “Fire away, Flanagan,” and the doughty champion took to his heels immediately.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
The phrase "Fire Away", meaning to go ahead and "Ask me questions" means to go ahead do your worst
used to give someone permission to begin speaking, typically to ask questions:
A: I want to clear up some questions which have been puzzling me.
B: Fire away.
Imagine yourself being a Glock 19
and your words (or your questions) are bullets.
Do you want to keep the bullets with yourself, or fire away?
away(adv.) late Old English aweg, earlier on weg "on from this (that) place;" see a- (1) + way. Colloquial use for "without delay" (fire away, also right away) is from earlier sense of "onward in time" (16c.). Intensive use (e.g. away back) is American English, first attested 1818.