Hi James and welcome. #4 Buck shot is a larger diameter than #4 Bird shot as viewed in this picture: .13" for #4 Bird and .24" for #4 Buck which is nearly twice the diameter. (3rd picture down):fieldandstream.com/outdoor-gear/guns/ammo/shotgun-ammo/buckshot-vs-birdshot ----------- Cheers and stay safe!

Hi James, #4 buckshot is larger and heavier than #4 shot, making it more effective for home defense as it delivers greater stopping power. In contrast, #4 shot is typically used for hunting birds and is not recommended for self-defense situations.
Stay safe & have a great day!