I just filled a CE2 v4 after vaping it dry and I was able to put in 0.8ml. Any more and it would start running out of the center hole.
With one that's totally dry I think I can get very close to 1.0ml.
I borrowed a condom end cap from one of my other cartos and put it on the battery end and this prevented any leakage during filling.
I got the RoyalSmokers from VaporJunction and they didn't come with end caps (condoms). Are they supposed to?
The newest R4's don't come with condoms anymore. Another reason to never throw anything away, no matter how small.