IIRC: Each barrel is just one long magazine. I don't think they'll get many customer's for it simple becuase it's a swine to relaod, and what goods 1,000,000 rounds in one salvo?
"well we killed that one bloke good and propper."
The Intresting Idea I did see involving this thing was to fire a huge number of indirect HE rounds in one go, a sort of super mortar, now 1,000 81mm rounds going off in one salvo, that would be scary.