I just now reached level 25 for gunslinger, and one of the first bugs I noticed for uber ammo perk was that it didn't seem to work with the m1911. It works flawlessly with everything else (dual magnums, dual deagles and single mag,deag) but with the m1911 it's bugged (both single and dual).
Hope this is fixed soon enough in the next hotfix/update.
Hope this is fixed soon enough in the next hotfix/update.