Thank you for the ID Smokey!It's a Williams Cleaner bullet. Nice find.
And prevented blow by with hot loads.While it has come to be known as a "Cleaner" bullet, that was not its original use. The harder zinc alloy disc was pushed forward into the softer lead bullet when fired, expanding the softer lead to create a tighter seal between the bullet and the barrel. That gave it greater trajectory, velocity and precision.
Williams patented 3 different versions of this bullet.
http://touchthepast.blogspot.com/2013/01/the-williams-patent-bullet.html