Drillings and Bockbüchsflinten (Over-and-Under-Shotgun-Rifles) are fairly often used in Germany.

I know two guys who own Bockbüchsflinten in 12/70 and 30/06. They report no problems at all. Anyway, I myself would always use a rimmed (flanged?) cartridge in a break-action gun.

Just remember, you can download a 30R to the level of a .308, but not vice versa. Also - if a 30 cal rimless - why not a 30/06?

Joachim