Good note, Micah. The denim here runs 6 ounce to 12 ounce. The 12ounce is what I use in the 14 bore rifle - measures .025" with the michrometer, and just over .030" with heavily squeezed calipers (between finger and thumb). The 10 works in all the rest of my guns, and runs .0225" for me, heavily squeezing the tines of the calipers between my finger and thumb.
We have found a blue, red and white mattress ticking, called railroad mattress ticking, that measures .023", is very soft after washing and loads easier than the denim, althogh another .0005" thicker. A number of us are now using this wonderful ticking as it works in about every rifle with a ball .005" smaller than the bore, ie: .395" (to .398" in mine) .445", .495", .535", .575". I haven't tried it yet int he 14 bore, but suspect it will probably work OK with the .684" ball.