The heart of the matter is that if you are in action the fewer things that you have to do the more effective you are. If you are in a close range firefight you really don't want to be fooling around with a bolt after every shot, all you want to do is aim and pull the trigger. That's why the Garand is the best of the standard rifles of WW2. The British Commonwealth was always behind the USA with weapon development. The .303 LE was replaced by the semi auto FN SLR but then the USA went fully auto with the M16. Eventually the FN was replaced by a fully auto rifle. The FN SLR was touted as being a superb weapon especially by those that carried it in action. The fact is that it is a shocker - too heavy, too long, you had to carry all of those empty magazines around until you could fill them and when being used to provide sustained fire in hot conditions it would experience stoppages due to being carboned up. There was a tool provided to expand the gas jet but from observations once it began to mis-fire there was nothing that you could do to correct this, other than to fully strip it down and clean it. And why did those who carried it swear by it - the average soldier has to convince himself that his personal weapon is best otherwise he begins to doubt himself as being effective.