On: FBI tells lawmakers it can't access Dayton gunman'...

[nickynickell]

I'd wager they meant drum. Though superimposed loads are a thing too.

[NikkiA → nickynickell]

And given that drum and barrel (when referring to containers) are usually synonyms in English, it's not unreasonable to imagine a non-english speaker confusing the two, remembering that 'barrel' is a term related to guns, and saying '100 round barrel'.