Here's the claimed performance from the acceptance meeting for the L11, in january 1963:
Here's the performance recorded in may 1963, when service ammunition was compared to identical ammunition constructed with a DU core:
And here's the results recorded in january 1968, when they tested DU nose caps:
So the limiting velocity for a 6" plate at 60 degrees increased from about 4150ft/sec, first to about 4250ft/sec just a few months later and then to 4460ft/sec or even beyond 4600ft/sec or so in 1968 - what on earth is going on? Admittedly they aren't using the same mark of ammunition - the acceptance meeting doesn't go into detail, but in the 1963 trials they used L15A3 and in 1968 L15A4 was used - however it's a surprising drop in performance for something that was supposed to be an improvement. AFAIK L15A3, A4 and A5 only differed in the materials they were made from, and not in the shape of the penetrator
So what's going on? do british rounds lose performance over time, or did they use wildly different testing standards somehow?