Ran across this handy online tool for determining the number of buckshot pellets that will fit inside a given inside wad diameter.
For example:
The inside diameter of the non-tapered BP CLBC wad is .620". The largest size for an even three pellet stack is .287".
http://www.engineeringtoolbox.com/sm...le-d_1849.html
This is also why a two pellet per layer stack works very well with conventional buckshot sizes.