I had a C. Lancaster double in .280 Flanged Nitro Express which had the oval bore rifling. I experimented with it a good bit over the years.

In that caliber, I found it to be quite sensitive to bullet diameter. If the bullet was the slightest bit undersize it would fail to stabilize. Using correctly sized bullets it was quite accurate. I bought some swaging dies from Corbin so I could produce bullets to suit it.

That's the extent of my experience with oval bore rifling.

You can view the rifle I used to own at this link.

Curl