I agree that a double should have the flexibility to fire either barrel at the user's choice, especially a shotgun. That is kind of the whole point with a shotgun. It may not be the case with a rifle. What I have run into is this. My current Double rifle, and probably my last, is a Frantz Sodia in near new condition. It is an O&U, I know it is not really a double rifle to many of you and you probably won't like the caliber either. It is a 348 Winchester.
With O&U you are recommended to fire the under barrel first to lessen the wear on the action. Something to do with the angle of forces based on the location of the hinge pin and lockup. I haven't measured this, I'm just taking a very experienced gunsmith's advice. If you shoot the under barrel first, front trigger, no problem. The only time I fired the over barrel first it doubled. I measured the trigger pull of the under barrel and it was significantly lighter and crisper than the over barrel was. Wondering if wear was causing this, I checked the engagement surfaces and observed new looking surfaces. It appears that at least this rifle was made that way. I'm thinking to make that first shot count as this is more of a stalking rifle than dangerous game gun.
The side by side doubles that I have owned and that I have shot that were owned by others never doubled and these ranged from smokeless to black powder and from 9.3x74 to 8 bore.
