slam-bang vs slap-bang

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

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

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

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

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