Heckler and Koch HK416.
Considered a possible replacement for the US Military's M4 carbine, the HK416 posesses a unique characteristic that distinguishes it from most other assault rifles -- it's cool. Literally.
Assault rifles like AK or M16/M4 operate using direct impingement gas system -- hot exhaust from the barrel drives back the piston that loads the next round and re-cocks the weapon. Direct impingement gas systems operate hot -- that is, hot exhaust gas enters the weapon's interior, polluting the bolt carrier group and heating it up, skewing the weapon's characteristics and increasing the chance of a jam.
HK416 is different. It uses a short-stoke piston that drives the operating rod that does the realoding and recocking of the weapon. This way the hot gases do not enter the weapon, and the weapon's internals remain cold. This means less cleaning, more accuracy and less chances of a jam.
I've actually seen this on the
Discovery Channel special -- the guy empties a clip into a target, then opens the weapon up and takes out the bolt carrier with his hands, showing that it is in fact cold. That is impossible to do with an AK or M16 or any of the "hot" systems.
HK416 has now seen limited deployment in Iraq (with Army Delta) and with some LEAs. Apparently, the Military had been looking into HK416, HK XM8 and FN SCAR for comparison with M4. We'll see which weapon system they select for the future. I'm sure Colt Defense, manufacturer of M4, is having a slow heart-attack. And they should -- procurement without competition is always a bad idea.
They say the semi-auto civilian version of HK416 called MR223 will be available in 2008. Too bad we can't freakin' buy it in NYC (classified as assault weapon and all that nonsense).