When buying patching material, it all about thread count. Cleaning patches just don't have enough threads per inch to make them strong enough for a shooting patch.
Oh, and by the way, when was the last time you guys "grabbed your dial calipers, and went to the fabric store". The fabric stores in my part of the country don't stock pillow ticking anymore. They get most of their fabric from out of the country, and only have a vague idea of what it's actually comprised of. They buy partial bolt, so you might get some, or you might get none. Now I will admit the only fabric stores in my area are of the chain variety, so a small independant store might serve you better.
Hungry Horse