sure as shooting is an adjective and adverb meaning "absolutely certain". It carries 2 recorded senses.
definitely or positively (`sure' is sometimes used informally for `surely')
“the results are surely encouraging”
“she certainly is a hard worker”
“it's going to be a good day for sure”
“they are coming, for certain”
“they thought he had been killed sure enough”
“he'll win sure as shooting”
“they sure smell good”
“sure he'll come”
colloquialism
Definitions, synonyms and semantic relations for sure as shooting come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.