Lord Jim wrote:but can the CHARM still effectively penetrate the latest MBTs?
Unfortunately no. At best it can function against Kontakt-5, since K5 was L27's goal to beat from the T-80U the UK acquired to study.
But there is a pretty easy scaling one can identify.
M829A2 was identified as being inadequate against Relikt by the US. M829A2 is effectively the same size/weight as the DM53/63. Similar properties.
The British Army themselves admitted that the DM53 from the smoothbore gun was more effective than the L27 from the L30A1.
Thus we can know that L27 is not adequate against the latest form of passive/ERA coverings, since the composite in the latest T-72s (T-72B3 onwards) has been significantly upgraded over the T-80Us time. A dart cannot penetrate composite greater than its own length in terms of RHAe, that's just physics.
One can argue "Oh it still could kill it if it hits here or here" but the point is about reliable, combat range kills, frontally if required that would constrain operations if it cannot achieve. The US is moving to M829A4 to counter this. The Germans/French...not so much on the Leopard/Leclerc at the moment.
The Challenger with the enhanced L55A1 though, as seen from Rhm now, would be capable of it too. It'd make the Challenger at least equal to the M829A4 used by the M1.