Not disagreeing KtK but I'd argue with the report that the protruding catch was a smaller area or that the pommell was either - or lighter! Nope..., I can't be bothered to weigh/measure but I'd argue that the pommell was lighter too, due to the large diameter hole bored right through it for the No5 rifle bayonet standard. Then ADD to that the cheaper but heavier metal grips.
The Major I mentioned earlier, Maurice Fogwell, who passed away a year or so ago was an absolute mine of info about the early L1A1 trials. He was also the person who 'signed-off' the much improved 7.62mm L4A2 and later L4A4 variant of the Bren and then later, the GPMG