Most gun post beat ups I have come across were over friendly forces in England, either on the aerodrome or local Army units. The beat up was normally without any weapons and would either be a pre-arranged "surprise" attack or practice for target tracking.
In the build up to OVERLORD many RAF ground attack squadrons would be tasked to attack military convoys in Kent Surrey and Sussex to give both sides practice. In one case it seemed that an armoured column was practice bombed and I suspect these were the frangible Bakelite bombs or cement bombs.
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