Wade,
Look at my article about elderberry wine making 2 years ago.
There are some pics there. Especially one where I have a complete screen in my hand.
http://wijnmaker.blogspot.com/2007/08/scroll-down-for-english-version-ik-had.html
Those are really ripe.
But be aware that the size is not a sign of ripeness as there are many different elderberry varieties and they indeed vary enorm in size.
I have bushes around here that have very small berries and bushes with berries that are like the ones in the picture.
Berries that are green or light red or brownish are definitely not ripe. They have to be black to be ripe.
You could do the float test (also in that story).
There is some discussion regarding the float test as european berries are likely different as US berries. But on another forum someone did some test and the berries that floated definitely had a lower SG as those that sank.
Luc