hello buckstix, you know this was build for the 75 gauge Eley needly fire cartridge.

https://www.gunsinternational.com/guns-f...un_id=101302686

there was also a 90 ga and a 110 ga cartridge
someone change the needle against a firing pin or it was simply worn out and look like a firing pin today.
you find an excellent solution to make a case that works in the chamber but imho, this rifle is blackpowder only.
the hollow base is a special Rigby improvement for this cartridges. the walls have an undercut and the later version of the paper case had a thin brass foil inside ( the british love paper and brass foil rolled together). when fired the base of the case was blowing out and stick in the hollow base of the breech. when open the rifle you can take it away with your fingers. the older version of this rifle with a plain breech had a seperate steel hook with each ammo box to remove the case because in this action the case was not blowing out of the barrel when fired. you need a special hollow breech like in the prussian military rifle so gas coming behind the paper case to get it out of the barrel.