Mike is illustrating exactly what happens in a barrel when an identical payload is propelled up a barrel in front of two powder charges of two different burning rates. One shell reaches 1200 at the 16 inch mark, the other reaches 1200 at the 20 inch mark. At either mark, the powder is exhausted. Yup, I guess the 16 inch shell will give us more felt recoil. However, not all of us will feel it, and if the powder were any slower in the 20 inch example, it wouldn't work as well in winter. As I said in an earlier post, we will use a powder as slow as it can be and still work in cold weather. What could be simpler?