Ahh, that sounds like the voice of experience speaking...tell us more
------- lil short barrel things need a load of weight, or resistance in order to have time to build pressure in the barrel and expell the load, just dont get carryed away with the amount of force on the patched projectile, that is why on a rifle there is such a thing as a bullet starter, once it is compressed it will slide down the bore better Mortars of bigger cal. and longer barrels work best with less powder, my beercan mortars have a bore of 2".620 dom the can is app, 2".600,not much of any windage as they say no need for a patch on these, with a load of 2 pounds or more the best performance comes ,, the more the load weight the longer time in the barrel and more pressure gets built up ,the longer it flys with less powder more of the same goes for 16oz cans, so i use course bulders sand and water for the load, i never have split a can, they sort of split when they hit the ground or a tree or the the ?target? going to try concrete filled someday , sand is cheep and easy , clean the barrel ,, CLEAN THE BARREL,