Ignore the paint remarks, they are just jealous (as am I). Those beauties will ring like a bell when fired. Good shootin'
My first beer-can caliber mortar (3/8" thick walls, coehorn powder chamber, HRS) rings when fired.
All the other mortars, 1" thick walls, calibers of golf-ball, beer-can, 24oz soda-pop bottle and 4" PVC pipe do not ring. It may just be that the others have a support touching the barrel at about the mid point.
When anvils were cast, the test for the integrity of the casting was to fill the bottom cavity (or the hardy hole) with powder and placing it on a solid base (like another anvil) to launch the anvil in the air; hence, the phrase "ringing the anvil" referring to the event.