Ross Seyfried wrote of a .303 single shot that ended up using .323 bullets. It was just way oversize.
Back in 1971 in Alaska, a state trooper gave me an old 7.7 Japanese arisaka 99. The stock had been butchered back to a short forend. "sporter". Original sights, straight bolt, etc.
So, with a alot of work and a little bit of gun smithing, Fajan stock, Williams receiver sight and front ramp, blade, lots of polishing and cold blue, It was my "big" rifle. Factory Norma rounds shot like shotgun paterns and sometimes tumbled. So, slugged the bore. Not .311, not .312, not .315. No, it was .317+. I produced a lead lap on an old rod and brush, lapped it out some more. used a fired case and a drill and more lap on the neck of the case to open the neck of the chamber a bit. And, to my inexperienced self, I had an 8mm (.318) / 7.7. I purchased nice norma 200 grain .318 diameter "J" bore bullets. Worked loads from the 8mm Mauser data to about 2500 FPS. It shot nice sub=2 inch groups at 100 yards.
I proceeded to take my first bull moose that year with the rifle. OK, I was 18 years old. Didn't know this wasn't the right things to do, but it worked out great for me!!
Fell in love a few years later and sold it for date money. Don't have the rifle or the first wife. Boy, I wished I had kept the rifle!