Everybody plays Blackwood.  Yet you shouldn't.  It is the most inefficient convention ever invented.  To check for a slam you want to 

•     be positive you both know what the trump suit is so that there can be no misunderstanding.
•     ensure you have the aces.  No ambiguous "1 or 3" that leaves you unable to be certain which.
•     be able to know whether you have the trump queen.  This can be a vital card.
•     be able to show specific kings.  Sometimes the possession of  the right king makes the grand slam, whereas another king does not.
•     be able to use the system and stop at the 5 level if you are missing aces, or at the 6 level if missing a vital king.  With Blackwood, minor slams are just a guess.  In pairs you might    "punt" a minor suit slam if you have missed the 3NT level, but you can't do this in teams.  Even in pairs, it is better to stop in 5 making than 6 going off.  Equally, minor suit grand slams are a pure guess.
•     have a convention that is above all simple, and easy to remember.

So, Blackwood is hopeless, RKCB is an improvement but still fails miserably.  What's the answer?

Take a deep breath.  You need a new asking bid.  You have been playing 4NT as the asking bid for so many years that it is a very difficult habit to break, but I ask you to try it.  People can kick the smoking habit.  You can kick the 4NT habit.

The Asking SuitThe asking suit is the suit, or next step, above the trumpsuit.  So the ace asking bid is the next step above 4 of the trumpsuit.  In a simple bidding sequence of 1♦  4♦,   4♥  asks for aces and agrees diamonds as trumps.  In the simple sequence of 1♠ 4NT,   4NT asks for aces.  (Yes, 4NT does ask for aces when spades are trumps!)

The Ace ResponsesThere are 5 aces, where the king of trumps acts as the fifth ace.

The responses are simple steps, and the general principle is that the"nothing to show" bid is (logically) the sign off in the trump suit.

       1 step     =    1 ace

       2 steps   =    2 aces

       3 steps   =    3 aces

       4 steps (= the trump suit)    =    0 aces

Nothing easier, the number of steps is the number of aces.

What does the teller do with 4 aces?  With 4 aces, you bid higher, immediately responding as if asked to show what kings you have. (See later)

This assumes that your partnership agrees that you will not ask for aces unless the asker has at least one ace himself.  And if he has only one ace, he will either have the queen of trumps, or sufficient trump length that the queen is irrelevant.

Actually, that is a slight simplification to make the structure obvious.  In practice, to allow for being able to show the trump queen, the responses are really

       1 step    =    1 ace     OR    3 aces without the trump queen

       2 steps   =    2 aces

       3 steps   =    3 aces and the trump queen

       4 steps (= the trump suit)    =    0 aces

       King response (higher bids)    =    4 aces

Finding the trump queenAfter the ace response, if the partnership does hold all the aces, the asker will ask about the trump queen if he does not hold it himself.

The queen ask is also used after the 1 ace reply if asker needs to know whether it was really 1 or 3 aces.

The asking and the replies are easy.

After the 2 ace response, if asker has 3 aces he may want to find out about the trump queen, and does this by bidding the next step. You simply sign off in trumps (next step) if you do not have the trump queen (the"nothing" bid).  If you do have the missing trump queen, continue by showing your kings as if asked. (See later)

After the 1 ace response there is more room ...

     If asker has 2 aces, with the queen himself, he in interested in whether teller has the 3 ace hand. Also, if asker has 4 aces, he is interested in whether teller has 1 ace with the queen of trumps. In either case, he will ask over the 1 ace reply by bidding the simple next step.

The replies are ...

       Next step (= the one below the trumpsuit)    =    1 ace and the queen of trumps.

       Sign off in trumps   =    1 ace, but no queen of trumps (the"nothing" bid).

       With 3 aces, bid immediately to show your kings. (See later)   (Asker would not be asking unless he held at least 2 aces and the trump queen. )

Over the queen showing response, if this shows possession of all the aces and the trump queen, asker can continue to ask for kings. If the queen is missing, asker can simply sign off at the 5 level.   He can, of course, bid the the small slam directly if he has all the kings, or an otherwise suitable hand.

If the asker himself has the trump queen, he does not need to ask for it and can simply ask for kings directly over the ace reply, if all aces are held.

The king asking bidAsking for kings commits you to at least the 6 level, so it guarantees all the aces.

Ask for kings by bidding the asking suit at the 5 level - the next step up from 5 trumps.

The king responses

There are only 3 kings, as the king of trumps counted as an ace.

        If you have no kings, sign off in the small slam (the "nothing" bid).

        If you have one or two kings, bid the cheapest king.

        If you have all 3 kings, bid the grand slam directly.

Asker places the contract, or if you have bid your cheapest king, he can find out about a different king by bidding that suit.  This says "what about this one - have you got it?"  If you have, you bid the grand.  If not, but you do have another king that can be shown below the small slam level, you bid that suit to show the king. If not, you sign off in the small slam (the "nothing" bid).

Note that when you bid the cheapest king it is the cheapest bid, not necessarily the lowest ranked suit.

e.g.

A                    xxx                    1♦    -    3♦

KQJx             Axx                    4♥ (ace ask)    -    4NT (2 aces)

KQxxx           Axxx                  5♥ (king ask)    -    6♣ (cheapest king)

AQx              Kxx                    7NT (that's the one I want)

That and the next examples show hands that cannot be bid by an old-fashioned quantitative king ask, but need the specific king.

A                   Kxx                     1♦    -    3♦

KQJx            Axx                     4♥ (ace ask)    -    4NT (2 aces)

KQxxx          Axxx                    5♥ (king ask)    -    5♠ (cheapest king)

AQx              xxx                      6♣ (how about this one?    -    6♦ (trump signoff) (=sorry)

                                                 6NT (pity)

Where the king is in the asking suit, obviously this cannot be shown by bidding that suit, so it is shown by bidding NT.

AQx               Jxx                    1♦   -    3♦

AQJx              Kxx                  4♥ (ace ask)    -    4♠ (1 ace)

KQxxx           Axxx                  5♥ (king ask)    -    5NT (cheapest king is the asking heart suit)

A                    Kxx                   6NT (pity he didn't bid 5♠)

Over 5♠ of course asker would bid 5NT to ask for the king of hearts.  Teller would bid the grand slam in diamonds if he had it.  Asker is not interested in the king of clubs.

Note that in the above hand, 5NT shows the king of the asking suit (hearts), and this is a cheaper bid that 6♣ to show the club king.  With 2 kings, you bid the cheapest.

Comments welcome        Ray Green