Personally I wouldn't use the cap as a measure. I would probably use the flask as a primer. In all honesty I don't think they would be very practical for loading, to many things in your hand.
The reason behind making one was just to see if I could work out the best method of getting threads in the cap at just the right place to let the cap tighten down against the body. I have been kind of fascinated by this style since I saw the first one.
Oh, it holds 75 grns, by the way.
Ron