Penetration with bird shot pellets and buckshot pellets is a function of the weight of the individual pellets, not the weight of all of the pellets in the load. If this was not true, then a one ounce load of No. 8 shot and a one ounce slug would have identical penetration out of the same shotgun with the same muzzle velocity. Of course we all know that no shotgun pellet, regardless of size, will penetrate as much as a slug.
NRA Life Member - RMEF Life Member - Vietnam Vet