In Europe gun licensing and ownership is so expensive that having the capability of doing more than one type of hunt with a single firearm is very advantageous. As much of the country is forested and shots are often from either fixed ground or elevated stands, guns capable of making rapid shots at close range are used. On some hunts, pheasants, hairs, boars and various deer might present shooting opportunities.
The option of having a shotgun, rifle and maybe even a .22 L.R. barrel on the same gun gave rise to over/under and side-by-side patterns of rifle-shotgun, drillings with either two rifle or two shotgun barrels on top and a single rifle or shotgun barrel under those or vierlings with a .22 L.R. or small bore barrel in the barrel cluster. The more barrels the more the guns weighed, but this weight made the guns comfortable to shoot.
In the U.S. the most commonly encounted guns of this type are the Savage or Stevens .22s/.410s two-barreled over/unders which were first introduced in 1939 along with the 3-inch .410 shotgun shell. Later models were made which used .20-gauge barrels with various rifle-caliber options. Although there were some historic three-barreled American drillings, such as Colt’s 12-gauge/ .45-70 from the 1800s, the first real influx of these guns came after the end of World War II, when GIs brought these home in their duffel bags.
Many drillings had 16-gauge shotgun barrels and rimmed versions of European cartridges. Mine happened to be an 8X57 JR Sauer&Sohn which took the older .318 diameter 8mm bullet rather than the 8X57 JRS which takes a .323 bullet. It is dangerous to use the wrong ammo in these guns. This fact is very well known to European shooters, but not in the U.S. Ammunition in both calibers was, and is, loaded by RWS in Germany and Norma.
Over the years my drilling has accounted for squirrels, rabbits, game birds, wild turkey, ducks, geese, deer and even a mountain lion. I had mine restocked to American dimensions with a beavertail forearm and recoil pad on it. It has been on many hunts and spent several field seasons in Alaska as a camp gun.
The more firing options there are, the greater the problem of making sure that you shoot the barrel you really want to discharge at the game. If this is your only gun, you will learn how to shoot it, but if it is something that is only picked up once every few years, it is easy to fire a rifle round when you really wanted to use the shotgun. The way to avoid this is to load the rifle barrel only when big game is in sight. You can do this silently with break-open guns. Do this, and you will not waste your hard-to-get rifle cartridges on inappropriate game or potentially endanger someone by unintentionally shooting your rifle.
When walking in the woods whcn you do not know if deer or small game might appear, a good approach is to load the left barrel with a shotgun shell and leave the right shotgun barrel (which uses the same trigger as the rifle) empty. This way you can activate the rifle barrel and have it or one shotgun tube instantly available. When only shooting birds, you keep the rifle rounds in your pocket unless you need it to kill an occasional mountain lion, as I once did.
I had one shotgun barrel of my drilling bored out to improved cylinder and left the other one extra full. This allows me maximum flexibility at close or more distant targets. Rifled slugs fired from my gun shoot two feet high when the rifle sight is raised. (Activating a sliding button on the top of the wrist arms the rifle lock and raises the rear sight on the barrel.) However, rifled slugs shot closer to the point of aim by sighting over the rib and front sight. Target different slugs and you may find one that will shoot at about the point of aim at 30-yards. With factory loads my rifle barrel shoots 3-inches high at 30 yards and is dead on at 100. I suspect that this was exactly how the gun was sighted.
Although my gun was not equipped with scope sights, this option is also available on drillings either using custom claw mounts or more modern mounting systems. A scope does allow more precise shooting at longer distances from a fixed stand, but gets in the way of making rapid shots at moving game.