Have made a huge crossbow today, chambered for the Cold Steel Short Assegai (actually the long version will fit, too).
See the Assegai on the Cold Steel homepage
Basically, a supersized version of the throwing knife shooter.
Total length is 220 cm (7,2 ft), weight is 8 kg (18 lb). A monster!
In order to master the huge draw weight (about 200 lb) and draw length (power stroke is 130 cm = 51"), you wrap the rope that is attached to the muzzle around a tree and lock the rope with a carabiner. Then you take the weapon between your legs and walk backwards, until the string locks in place.
Then you secure the front "tree" rope and load the Assegai from the muzzle side.
The power is absolutely phenomenal. It went clean through the double straw mat (that holds back arrows shot from 70 lb compound bow), and stuck in the wooden shed wall. It fire WAY harder than you can possibly stab or throw the weapon.
I think this is about the biggest crossbow that is still somewhat portable! Great fun. Will do the video tomorrow.