Source: www.vba.asn.au        

The standard responses to 0314 RKCB are as follows:

4 4NT Assume  are trumps
5 0-3
5 1-4
5 2 (or 5) without Q
5 2 (or 5) with Q

After 5 or 5, a step bid is then used as a trump queen ask. The standard responses to these are:

4 4NT Assume  are trumps
5 5 5=Asks for Q
5 No Q
5NT ? I don’t know what’s «standard»
6 Q with K
6 Q with K
6 Q with K
6 Q with no Kings

There are two major problems with this:

(1) 5NT is not utilised.

(2) If opener bids 6 with Q and no other Kings, how can responder investigate a potential grand if responder wanted to ask about 3rd round controls (such as a vital Queen in a side suit, or maybe a doubleton)?

I am uncertain as to why 6 is taught as the bid to show the Q with no side kings because it doesn’t make much sense to destroy so much bidding space when responder could be looking for a grand even without the aid of other kings.

A much better improvement would be to use the 5NT bid as the «Q with no other Kings» so responder still has all of the 6-level bidding to investigate third round controls. No doubt this is not the «best» version of RKCB available but it is certainly a better improvement than what the standard/default responses are.