If you want guarantees, then hunting dangerous game is not for you.

Talking as tho a hit with the second shot must be "guaranteed", shows no appreciation of the benefits of the double. Probably the only certainty that you have, is that there will be the odd occasion where the man with the bolt-gun will not have enough time to get off an accurate second shot AT ALL.

At the ranges under discussion, hits with the first shot say little to nothing about the merits of the action.

Those who say that a double cannot be reloaded quickly have obviously never seen it done by a practiced hand. Just like shooting quickly and accurately, it's a skill that requires practice. But that doesn't mean that it can't be done. Just that you haven't done it.