OTOH, and I have no idea what Bro. Bruette is saying
Dr. William A. Bruette,
Guncraft: Guns, Ammunition, Wing & Trap Shooting, 1912 (Editor of Forest & Stream)
https://books.google.com/books?id=5g51K93as84C&dq
“Cause of Bad Patterns”
https://books.google.com/books?id=5g...4C&pg=PA100&dq
The most general cause of bad patterns is tightness at the nose of the chamber, whereby the exit of the charge is impeded, and the pressure of the powder is accordingly increased. When the chamber is right and the shooting is bad the next thing to examine is the form of the cone joining the chamber to the 12-bore part of the barrel.
This should be of not greater length than .25 of an inch, and the slope should be a true taper from the nose of the chamber to the barrel.
When the cone is excessively long the column of shot is apt to widen so as to occupy the greater diameter beyond the cartridge. Its subsequent compression to the diameter of the bore jams the pellets together, so causing a tendency to ball, or at any rate to deform them so as to interfere with their regular flight after leaving the muzzle.
Threaded Mode