I don't know Mr. Willis, and I stumbled on his website by accident while looking up the definition of "overall length" as to dovetail cutting bits for milling machines. I happened upon his discussion of OAL as it applies to reloading rifle ammo. I thought it was pretty informative, and he has an innovative product, so I thought I'd pass it on. Take a look, in particular, at his "tech tips" page about halfway down the menu on the left.
http://www.larrywillis.com/
http://www.larrywillis.com/