Oh, I understand with solid projectiles, reducing the diameter slightly to allow some sort of barrier - I just don't see using grossly undersized bullets in a large bore and thus reducing power.

The Lyman sabot moulded slug is a good idea - the 'slug' is only reduced to about .68 cal. from .73, but to grossly reduce the diameter to the .50's is to lose a great deal of killing and stopping power.