Not sure how it works with a dog (I’ve never had a chance to hunt grouse over a dog), but I recall several times where a grouse was flushed, one shot fired, then a second grouse flushed (I learned not to break my gun open too quickly if my second barrel was unfired).

I also recall, on at least one occasion, firing my right barrel too early and my left barrel too late. In those cases, I just knew if I had a middle barrel I would have connected. 😆