When they are on the ship firing at the bad guys, they never load up a clip for their guns, and you never see where they get their clips from...they kinda appear from nowhere.
A)at the start of the scene you see oconnel packing some serious weaponry
B)He changes weapons at regular intervals
&
C)They all had revolvers as pre-stated
No they didn't. Burns (the guy with the glasses) was shooting with a semi- automatic pistol, probably a .45. And while we're on the subject, another strange thing: you can see that the said gun runs out, but for some reason he keeps making the shooting action even though his gun is empty!
Plus, the Magi thugs on the boat all use Mauser machine pistols.