I have to agree with Mikey.
The limited experience I've had with economy-grade double rifles has been unfavorable. The expensive ones are regulated by the maker for ONE factory load, and nothing else seems to shoot well in them. A couple of friends and I have spent many hours trying to develope accurate loads for double rifles.
I suspect it has to do with the way a double gun is made. When the barrels are "regulated" to shoot to point of aim with one factory load, the barrels are soldered in place, just like double shotguns. All that heat must do SOMETHING to the straightness of the barrels!
At any rate, I count the big-bore double rifle as strictly a short-range proposition, when that second shot is important or vital. It's not for show-off quality groups at 200 yards!