Short article but with advertisements for the thin brass cases designed for the "chamberless" guns
https://www.oldammo.com/january14.htmThe chamberless gun was developed in the 1920s by Dr. Charles J. Heath, a British surgeon and water-fowler. Dr. Heath determined that using a thin walled solid brass shell eliminated the need for the heavy forcing cone that was required on a gun that used paper shotgun shells. Removing this cone allowed the bore to be enlarged to about the same size as the inside diameter of the brass shell. Because these brass shells had such thin walls, they held more powder and shot than a paper shell of the same gauge, but also required that a larger wad be used. An added benefit to removing the forcing cone was that
it significantly reduced the recoil of the gun. (or not
)
I have not been able to find the Heath patent, but more on Heath from the IGC
https://www.internetgunclub.com/forum/viewtopic.php?t=63 Another thread which briefly touches on the chamberless concept
https://www.trapshooters.com/threads/don-currie-on-forcing-cones.894688/And worth mentioning, Stan Baker's maximum 12g "Big Bore" was .800" which is essentially the end of the chamber dimension (Hunter Arms' engineering drawings showed .797" ), ergo no forcing cone.
