Most of the pictures are of tubes for 107mm rockets of which there are 1000s of in Syria. The alternative is laying them on the ground and using sandbags or rubble for elevation. A tip is that if the ‘butt’ end isn’t way lower than the ‘muzzle’ it isn’t a mortar. A 4” hole in the pipe and a battery will be a rocket launcher. Pretty good milling for the 82mm mortars, I wonder what they use for explosive fill. Recycling from other shells would be pretty exciting.