The Norma 6x70R (based on the old 6,5x70R "pencil" case), is also known as the 6x70R Rehwild, meaning "roe deer" and was introduced to the market just a few years ago. The name makes it pretty clear what it's target is; Europes must hunted deer.

To use an insert cartridge, you insert and lock the light muzzle-length barrel insert into a break-open shotgun bore. It's actually a bit more complicated than this because of the issue of different chokes, forcing cone shapes and barrel lengths. So normally the insert is made to precisely custom fit just one barrel of one break-open gun like a Drilling or an over/under combination rifle/shotgun. The insert is also indexed to that particular barrel by having it's extractor fit into a precisely milled out slot in the parent bore's extractor, so it piggy-backs. Usually the insert is placed in the RH barrel of a Drilling as these typically have a set trigger. The shotgun striker fires the rifle cartridge.

The 6x70R offers a small gain on the .22 Savage,(5,6x52R) which is also a popular insert cartridge choice because of relatively light back-pressure. Other possibilities are the 5,6x50R and, for predators like fox, the .22 Hornet.

The idea, by the way, is to get the insert in a scoped Drilling to group at 100 m to the same POA more or less as the big game cartridge still available to shoot in the Drilling, a 7x65R or similar. The way this is achieved varies with insert designs but one type has screws at the muzzle which are adjusted to bring the POI up, down or sideways. I'm told, (can't vouch for this), that it does this by actually bending the insert barrel in the middle. So you now have 2 choices of rifle immediately available to match the game - or you can remove it for double-barrelled wingshooting.

These inserts used to be somewhat shorter, 44cm for instance, but the problem was that they had to be removed from the shotgun bore to allow cleaning of that bore after firing. When replaced and re-locked them into place, they really needed to be resighted. By making these inserts muzzle-length now, the fouling problem has been averted, but now there are issues with any moisture that gets trapped between them and the shotgun bore. So proper water-proof sealing of the bore is also important if they are to be left there for any length of time.

My understanding is that Norma market 6x70R brass and I see that this is available from at least one US source. If you're buying a new Krieghoff combination gun, you could have such a insert fitted. You could buy the insert seperately, but who will custom fit it outside Europe ? Or you could import a gun from Europe and specify you want such an insert fitted beforehand. Or you could use a 6x70R barrel on a single shot. But do you have roe deer sized targets ?