Plastic was employed in CanadianBren accessories production from Nov 43. From notes held at Warminster.
'Plastic used for Canadian produced Containers Oil and plastic tips permitted on Canadian produced spare parts wallets and holdalls. Zephyr Looms and Textiles. November 1943'.
I don't think that this info made it to the gun crews who carried the stuff in action or arms storemen who refilled the SP wallets and holdalls, the QM's who indented for the stuff or Ordnance who stocked and supplied it. Or, lastly, the Armourers shops who maintained it all
There were a few pages of relaxations allowed in Canadian production. For example. 300 barrels destined for scrap due to flash eliminator slots misaligned. 200 just machined down (barrel shortened by .25") to machine away incorrect and remachine slots correctly. 100 had re-aligned flash eliminators fitted. Dec '42
WHILE we're here, another one from the copied files. Browning process replaced by phosphating and painting in production '.....will commence during April '43 during the change in gun production'. This could possible be during the change from Mk1m to Mk2 production which commenced then