A couple suggestions for improving the current mechanics for scarface:
(1) Remove the 80% cap on his chance to proc another hit, but make the percent chance to proc be reduced for each additional one. (Like multicrit, but perhaps with a .9 modifier)
(2) Alternatively, you could remove the 80% chance, but cap the number of additional shots at some fixed number. (Sort of like the gatling gun in youTD)
(3) Or maybe both of the above?