This is rather odd, I've seen these drums and wondered the same.
I still have a jug of R11 myself actually, around 22 lbs, however it's jug form and has a standard 1/4" on it which makes it useful.
Make sure to charge by weight.
R123 I've heard is rather good stuff though from an efficiency point of view, it's got greater uses in the autocascade industry though. It's sort of like a super sponge, not as good as R11, but we're told to avoid touching that these days.