What Curl said!

With respect to bwananelson, I would have a good think about whether you should put a primed case in the 2nd barrel to test whether you 'double' or not. Others have found that with certain action types (non-rebounders, I guess), the firing pin is not pushed back out of the primer by the pressure of firing, and the pin can stick in the primer and lock the action shut. If this happens, you may need to remove the LHS lock and manually withdraw the pin, or if a boxlock, remove the floor-plate and manually re-cock the left tumbler with a screw-driver or similar.

It's easy with an ejector, just put a snap-cap in the left barrel and see if it spits out when you open the gun!

BTW, I'm groaning too! ...but I do use the left barrel for deliberate single shots when I remember, as in a finisher when the quarry is down.

Just a thought: those of us brought up on bird-shooting with SxS shotguns have fired literally tens of thousands of rounds in a lifetime and never doubled once!