bluntly vs flat out

bluntly and flat out both are adverbs.

Word	Noun	Adjective	Verb	Adverb
bluntly	No	No	No	Yes
flat out	No	No	No	Yes

As adverbs, bluntly and flat out are synonyms defined as:

Other synonyms of bluntly include bluffly, brusquely, roundly.

bluntly (adverb)	flat out (adverb)
in a blunt direct manner	in a blunt direct manner
	at top speed