Tired of looking at sectioned bullets? Let’s look at a butt. 50-70 Govt., copper cased, this is the 2nd type Martin Primer with the re-entrant fold at the rim.
BTW, I’m not being a dirty old man. In Benchrest we call the base of a case the butt. We cut our chambers so that there is very little expansion upon firing and this we call, a “tight butt.” Really. :) :)