I agree on KGV class guns to be quite green and troubles to be expected. In any case Rodney, despite having to turn several times in front of Bismarck (thus blinding her all-fore turrets) was able to fire more, heavier shells, having 1 gun less, and being much closer to the enemy. I expect she was the Bismarck's "killer" more than KGV.
you wrote: "After all first ~30 minutes of firing gives no trouble on KGV. ( on PoW problems were from begin but she was quite new, and had no real exercise before action)......"
The only reason why KGV had problems "only" after 30 minutes on May 27 was that she turned sharply for the first time (180° to north at 9:18) and at that time the quadruple turret jammed.... In the same way, PoW turned 160° to disengage, after 9 minutes of quite fair shooting, and her quadruple turret jammed.....
I don't really see any difference between the 2 ships due to training level and still I'm not convinced that the problems were ever 100% solved on the class.
We are going perhaps out of topic, but in case you are interested, there is a thread where we have already discussed the aspects of KGV shooting on May 27: http://www.kbismarck.org/forum/viewtopic.php?f=1&t=6834 and another one, where we have analysed the PoW vs Bismarck firing on May 24: http://www.kbismarck.org/forum/viewtopic.php?f=1&t=6811&start=450