As I understand it from the L8 trials and the L8T trials, the 'problem' was all to do with the barrel length and weight ......, or lack of both! If anyone can elaborate on that.......

It's interesting that even for the heavy barrel L4 guns, the barrel length and weight was finely tuned before it could be used to the extent that many thousand unused .303" Mk3 gun barrel blanks couldn't be utilised in the programme