I read in another thread that this rifle was going to weight 32 lbs and has a 36″ barrel. To put this in perspective: the caliber, barrel length and weight are very similar to smaller swivel cannons!
I am not sure if this is a true rifle or a paradox gun (mostly smoothbore but rifling near the muzzle).
A few more photos of the rifle (click to expand):
The owner was considering a load of 275 – 325 grains of blackpowder firing 3500 grains of lead.