We were talking about primer and powder, I thought.......perhaps I misread......
As for the 12 ga and the wall.......even a cylinder choke would not allow the shot charge to open up much in the 10 or 12 feet across a room, it still hits as a mass and penetrates thoroughly......and barrel length is not a factor.......the charge in a 12 ga shotgun pretty well reaches maximum velocity in 20 inches.
Petros said, "And yes even with just a primer it will go through drywall. get real. "
Dasleeper said, "Obviously you have never handloaded or experimented with guns
With just the primer a bullet will bounce of a rubber target holder 40 feet away.....when it reaches it "
To which Les said, "lol, by the time the wadding from my shotgun reaches the muzzle after being propelled by primer, it's slowed down enough I can hold my hand in front of it. If I had a 12 Magnum, it might even hurt a little."
I love solving puzzles.
Um, Colpy, length of barrel does have an effect on grouping of the shot (as well as the choking). The shorter the barrel the wider the group. Kind of like the difference between say a .303 silhouette gun and a .303 hunting rifle. You'll be more accurate with the rifle and have a better grouping.