slap-bang vs slam-bang

slap-bang is not an adjective while slam-bang is an adjective.

Word	Noun	Adjective	Verb	Adverb
slap-bang	No	No	No	Yes
slam-bang	No	Yes	No	Yes

As adverbs, slap-bang and slam-bang are synonyms defined as:

slap-bang (adjective)	slam-bang (adjective)
	violent and sudden and noisy

slap-bang (adverb)	slam-bang (adverb)
in a violent or sudden or noisy manner	in a violent or sudden or noisy manner
directly or immediately	with heedless speed
	in a careless or reckless manner