Doubles in 9.3x74R are available off the shelf, rather than trying to build something. They need not even be all that expensive. I had a Baikal O/U for example, which actually proved very reliable and handled and shot well. I shot a good number of critters with it including several truckloads of our buffalo. Baikal also made a .45/70 SxS - which I think might be what mauserand9mm pictured.
Alternatively, if you want something which can do for deer as well as grouse and whatever, why not just get a combination? Something like 7x57R/12 ga does a fine job, for example, and there are any number of options available in this or similar combinations of rifle calibre and shotgun gauge. Before I bought my drilling I had a Brno ZH300 series in that combination, with a second set of 12/12 barrels. It worked very well, giving an instant choice of rifle or shotgun barrel when in combination form due to having dual triggers. I shot everything from rabbits to birds to deer and pigs with it. It wasn't perhaps as light as it could have been , but was very stout.
There are others too - though I'd recommend steering clear of those which have a single trigger and require you to manually select each barrel, especially those with an external hammer. I've tried a couple of such guns, and you give away an awful lot of the versatility.
