The M60 GPMG. In Australian service it was defeated during the competition to replace the Bren LMG by the FN MAG58. A political decision was made by politicians to allow "interoperablity" with US forces as so we ended up with the M60 GPMG. The M60 in turn was replaced by, guess what? The FN MAG58 in 1989... A decision that was based upon reliability and ROF.
The M16 series of rifle in Australian Army service. Chosen, during the Vietnam War to replace the Owen SMG, the M16 was in many ways a disaster. It was unreliable, it used to spit magazines when firing blanks and it used to foul excessively with it's Llungmann direct gas impingement system. It should have been abandoned as soon as it appeared on the scene but it wasn't. Thankfully it never replaced the service rifle the L1a1. A favourite amongst the gun boys and the SASR simply because of the Gucci stuff you can hang off it.