Getting Faked Out

A K 3
6 5 3
K J 10 2
K J 2
Q J 9 7 5 10 8 6 4
2 J 8 4
8 A 9 5 4
8 7 6 5 4 3 10 9
2
A K Q 10 9 7
Q 7 6 3
A Q Vul: N-S

NorthEastSouthWest
1 NT Pass 2 Pass
2 Pass 3 Pass
3 Pass 4 NT Pass
5 Dbl All pass

NorthEastSouthWest
1 NT Pass 2 Pass
2 Pass 3 Pass
4 Pass 4 NT Pass
5 Pass 5 NT Pass
6 Pass 7 All pass

Wow! What a disparity in these two views of the potential here. One pair doesn't feel confident enough of a 5-level bid to redouble, while the other goes for all the marbles with a grand slam bid -- missing an ace. It's true that the disparity was only two levels, but those are a big two levels, the most dramatic in the bidding scheme, magnified by the fact that each pair had all the world to explore for their potential without interference from the defense. And speaking of the defense, they had their marked disparity also, one defender, at least, figuring on at least 3 tricks when his side can't inhibit an overtrick in that denomination, while the other pair declines to double the grand slam, even though one defender on lead has an ace in a suit both defenders had bid! I dunno.
Anyway, I thought I would put this into two categories, while leaving both bidding schemes for what they're worth. As for five diamonds doubled, well, you're getting faked out of a slam if you get nervous at the double, perhaps figuring you're going to get an awfully bad trump break. Actually, it pays the defense to suck you into quitting at the double -- unless you redouble. So above, where I said one defender expected to pick up 3 tricks, I thought as I was typing it that conceivably this was a savvy player who had faked out others with a 5-level double. In any event, let's look at the scoring system:
If you've got slam in a minor suit, vulnerable, that's 1370. This declarer, picking up the overtrick, got 950. But if he redoubles, he gets 1400, barely beating out those in slam (undoubled). (He would get 500 for the game, 400 for the trick score, 400 for the overtrick and 100 for making a redoubled contract.) The incautious defender gave his opponent a chance for a good board, and a bit of insecurity turned that into a bad one. Now there are still a few loose ends here. One is the presence of an apparent major suit slam, which would have been better than 5 diamonds redoubled. To be sure, 6 hearts can be beat on a diamond opening lead and continuation, but the bidders couldn't know that during the auction, so it would be understandable if they would spurn the redouble of 5 diamonds for a heart slam -- or better still, a no trump slam, which neither pair seemed interested in.
So let me tidy this up with a few pointers:
    This is strictly for when you're slambound, as the bidders above were. I'm not suggesting that you double all five level contracts. I'm saying that if you really think there's a good chance for slam, the five level redouble, if available, will bring you more points than will a slam bid.
    There are no guarantees here. People have been known to go down 2 in slam bids. Nevertheless, I am saying it will by and large do you well if your bidding has been reasonable and sound, and that you can't afford to let that double scare you off. And you have a one-trick cushion for bad breaks.
    But you must pick up that overtrick, if available. Just because you make with 11 tricks doesn't mean you've got a good board if 12 are available. That overtrick is an integral part of the bonus.
    This doesn't work if you've got grand slam. You have to bid it. But it will work in you're doubled in six! Six hearts doubled and redoubled would be 720 plus 750 plus 500 plus 100 plus 400 (for the overtrick) for 2470. To put this another way, sacrificing 750 in slam bonus, you pick up 3 times trick score or 540 for the redouble, plus 400 minus 30 or 370 for the 13th trick, which is 710 right there, and 100 for making a redoubled contract. Five hearts doubled and redoubled would miss 1500 in slam bonus, picking up 450 in trick score, 800 in overtricks, minus 60, plus 100 for making a redoubled contract, and it won't do.
    It won't work in a minor suit if you've got a major suit or no trump slam, as mentioned above.
But it'll work if your vision of slam has been reasonably sound.