What was the original pronunciation of 'Zounds'?

At the time this imprecation was common wound was variously pronounced, with either /ɑu/ or /uː/,^† so both pronunciations are attested. OED 1 reports these spellings: ‹zownes›, ‹zoones›, ‹'zons›, ‹zons›, ‹dzownds›, ‹sownds›, ‹zwounds›, ‹zauns›, ‹'zoons›, ‹zoons›, ‹'dzwounds›, and ‹zounds›

^† Regular sound change would call for wound to end up the same as bound and found and sound, as indeed the participle did; but the rounded /w/ at the front interfered with this development. The language didn't settle on /wuːnd/ until the 18th century; in the 16th and 17th centuries both were available. Compare R&J, at the artificial boundary between 'II.i' and 'II.ii':

BEN:             ’tis in vain
To seek him here that means not to be found.
ROM: He jests at scars that never felt a wound.