Assuming a good checkout
by a qualified doublegun smith, (and they're not cheap,) then you'd likely need to investigate either blackpowder loading or the newer, "nitro-for-black" loads. Most (consider that to mean "all", unless you're sure what you're buying... and if you didn't have to special-order it, it ain't the right stuff) commercially-loaded ammo will develop pressures too high to be safe in older European double guns.
That's not to say that they're not safe to shoot, although many are not. It's just that shotshell loads are much higher-pressure than they were a century ago, and the older guns won't take the abuse.
Loading for and shooting older double guns is not a tyro's game. You really, really need to know what you're doing, and the only way to learn is from those who already know.
A trip to Wally World might well cost you a thumb.
You only get two.
--Shannon