I think you mean #4 Buck.
0000 Buck is 0.380 inches in diameter.
http://www.ballisticproducts.com/Super-Buck-Lead-0000-8-lb_jar-380/productinfo/SBK40/
I have mine loaded in #4. Nice size, about like a BB.
What are good loads for a .20 gauge? One for home defense, the other for birds (quail, pheasants, etc.)