@ Anonymous Coward
"There are plenty of reasons to fire more than 3 rounds in a burst, and us English with the L85A2 trust our soldiers to choose when to use each fire mode, rather than restricting them to burst fire."
Actually no they don't. I AM a soldier in the British Army and automatic mode on the L85 is restricted in use unless your in very specific scenarios and even then you are trained to keep your bursts to approximately 3 rounds or less to prevent recoil climb. The M16A4 was an example I gave because that specific generation model appeared long after the L85 was designed and thus incorporated more enlightened thinking and also offers a way to limit the recoil. The original M16 had full auto too. I absolutely promise you by the time you have fired about 6 rounds from the L85 your rifle is pointing a good deal higher than where you aimed and will only continue to climb.
"Also they claim to have fired the weapon at 1100 degrees, so assuming this was done using a hand portable prototype, I assume they've overcome any other heat build up issues in the breach."
That's all fine and well if they have machined a NEW weapon or re-engineered an existing weapon for the barrel. However it's not a case of simply fitting the new barrels to existing weapons as the machining tolerances are not designed for constant fire. Plus I absolutely guarantee you put a round into the breach at 1100 degrees and it WILL cook off (Regardless of whether or not it's an open or closed bolt weapon). And with the current SDSR in place, I highly doubt we will be swapping our weapons out anytime soon.
All this is aside from the fact that automatic fire in an individual weapon is rarely used because apart from being up and close and personal, it's not effective. Single aimed shots are better. As for support weapons, well in a real contact you would simply never get the opportunity to fire at the weapons full cyclic rate. Ever. Even if the weapon is mounted or bipod based.
I'm not saying they are a bad thing, not having to carry and swap out a second barrel would be a great thing (And I speak from the heart having been an LMG gunner in Afghanistan) but there is no way that they would lead to any military switching its training or operating policy to one where you can blaze away (Or "hosepipe" as we refer to it. Imagine the rounds from the barrel as a stream of water from a hose).