Actually, a semi-auto shotgun is good enough. BTW, blowing off some loose gunpowder in ‘can’ makes a big noise. The real effect is when you compact and compress it, then explode it.
Hate to be the bearer of bad news but smokeless propellant does not explode. If it did, the projectile wouldn’t exit the barrel.
But probably the easiest ‘bang for the buck’ is firecrackers in a cooking pot.
I learned that from a kid named Kevin. Very polite young man.
Back in the Good Old Days, they used to pack black powder too tightly. With lack of air the early siege cannons lacked much punch. Then they learned to ‘corn’ the powder so that more ‘air’ [actually oxygen] could cause it to ignite more rapidly. Much better blasts with less cost in sulfur.
Took them over a century to figure that out.
‘Actually, a semi-auto shotgun is good enough.’
I should hope so for home defense! But I did read about a fully automatic shotgun used by the military. Loaded with a drum if I remember correctly.
Only thing, I thought that shotguns violate the Geneva Convention. So maybe mercenaries? Dunno.