this punt gun with a snider action belongs to a friend

gun started as muzzle loader and was converted by John Padstone Southampton. its coming from ireland some years ago.
I was making cases for this with once fired 23x152 Belted Russian machine gun steel cases.
The chamber of the punt gun shows an unknown cartridge :
40mm rim
36mm base
33mm mouth
155mm length

the 23x152 B:
35mm belt
32mm neck
length till beginning of the neck 120mm

I turn the base of the steel case so it accept a 40mm steel washer and welding it together.
Drill a hole for a 209 shotgun primer into the case and anealed the neck.