Here is some thing you could try , I have a old Lee Speed/BSA sporter , the barrel is shot out & bullets tumbled badly at 25yds , I also had a Cape Gun - 303X12Ga SXS , it's barrel was shot/rusted out , I was going to rebore to 9.3X74 or 375 of some kind , any way some one on one of these forums said to try 8mm/318 bullets in that , I got some , but the Cape gun was too buggered all over so I shelved the slugs.

On shooting the Lee Speed & seeing the massive group/pattern of Key holed bullets I remembered the 318 bullets , made sure the were a loss fit in a fired case (so neck can release bullet in chamber when fired) loaded them up and shot this group below !

You will want some thing better no doubt , but you can try this to get the old girl hunting again ?

Cheers !

Oh! Could you share some photos of her please ?