I'm pretty sure I heard that when 'They' played the part of OPFOR on certain exercises they would use adapted LMG mags and the auto trick. That said, I came across a load of 'Them' on exercise near Longmoor and they were all using Chinese (I Know because they told me) Type 56 so presumably it would be easier to draw these rather than bugger about with adapted L1A1s.Recruit battle camp somewhere near Aldershot in 1984, one of the DS applied the matchstick shim when playing enemy troops. Same size round/noise as the GPMG, but at the speed of a buzzsaw scary shit. Difficulty with the match stick was that it could wear and you lost trigger control, so what was left in the mag went down the barrel.
He and a couple of others had been in the Falklands and were kind enough to fill me on on their experiences on the wrong end of the Argentinian FN full auto experience.