Bob Brister's "Shotgunning, The Art and the Science"
Don Zutz - "The Double Shotgun"
Jack O'Connor's - "Shotgun"
And a bunch of others. Go to the library - yes they still exist - and look, or do an internet search and do a lot of reading. You Tube videos of teenagers blowing up watermelons I do not find very beneficial. YEMV. Good luck.