Spot-on Brian and Wingshot. To improve is the goal. After being in the sport for a while, you will learn there are "prescriptions", so to speak, that will work well in most rifles and smoothbore. The results vary, of course as all guns require slightly different combinations to achieve their best performance.
What we've found is about .018"(8oz. Denim) is the thinnest we even try. I prefer 10oz. Which I measure at .0225", however the last 10oz. Denim I bought is only .020" with the same measuring device. I expect it will work in all.my guns except for the .69 which has always preferred 12 and 24oz. Denim (.030 & .034")