A double rifle is a different proposition than a double shotgun. The shotgun is working within a very limited effective range, close to the gun. Depending on the chokes and the target this will only be from about 15-20 yards to 40-50 yards. Closer and you mangle your meat, farther and you cripple and lose too many birds. The rifle is expected to be effective out to a much greater range, sometimes two, three or more times as far and they are expected to be much more precise. All double rifles have been and still are regulated to put a specific load fired from both barrels into a composite group, on point of aim, at a distance specified or set by the gun manufacturer and this applies only with that one load. Closer than the regulating distance, which will vary by caliber and the preference of the manufacturer, and the left and right barrel hits will be separated, by the muzzle centre distance at the muzzle down to complete convergence at the regulating distance where they will cross and start increasingly separating again as the target distance increases. This traditionally is a very time consuming trial and error process that can involve many trips back to the shop for adjustment and subsequent retesting for effect. It works, but the shooting technique must be precisely consistent shot to shot. For that one load in that one rifle. Change any parameter of that ammunition, bullet weight, bullet profile, bullet composition, powder type, velocity, pressure, different shooter, different techniques and you’ll be starting all over. If you are looking for composite groups the size of your palm in a .577 at 50 yards to pot an elephant the challenge is completely different than for a 7mm rifle for hunting deer, goats and sheep at three or four times that distance.
Careful experimenting with different factory loads, different reloading combinations will allow an owner to tailor his ammunition to his specific double rifle within limits. As a basic guide, heavier bullets normally print higher at the regulated distance and will frequently shoot apart as well and this varies by weight. Slower velocities usually result in converging barrel impacts, higher velocities spread the velocity impacts horizontally. New double rifles regulated for modern readily available ammo can be very accurate with the specified ammo, vintage guns can be a near endless source of experimentation and frustration because of the lack of original ammo or the correct components to make your own.
