The Piggies didn't arrive... and the cold is bad.
Will try to make the how-to about the assault slingshot crossbow this weekend, but the work is going slow due to the nasty cold.
I will shape the weapon much after the Steyr AUG 77, one of my favorite designs. Just over 60 cm total length (24"), very very compact but powerful, due to the rollers and the bullpup design. Every inch of the weapon will be used for the acceleration of the ball.
I think there will be a time before and after the release of this how-to... finally, a short, powerful and accurate sling-x-bow that everybody can make at home, with very few common tools and a bit of plywood.