The #4 Buck loads were a hot ticket a long while back, plenty of pellets and even patterns. However, they fell out of favor due to lack of penetration at a distance. They kicked like a mule, too.
I note that Federal is offering a reduced recoil plated #4 load these days. This might be a pretty good load for strictly indoors use. Lots of pellets and limited over penetration hazard perhaps. Does anyone have testing or data that reveals the maximum distance #4 Buck will meet the 4 layer denim penetration standard?