I just got some West Systems 650 Gflex, per the instructions you mix it 1:1 by volume. I called tech support and asked if you could measure by weight- he said it wouldn't make enough of a difference to worry about.
I am very interested in making an auto myself, and here's what I can add-
The book "Knife Mechanisms just for the fun of it. " by Leroi Price has several auto designs and a bunch on assisted openers. You can find it here-...