MOOORE!
"Its light weight makes shooting it standing up almost as easy as lying down."
"Rate of fire is lower than the incredible 1200 rpm of the MG3. HK121 can fire in three different modes: 600, 700 and 800 rounds per minute. Rate of fire can be changed quickly and without any special tools, just by changing the amount of gas released."
Read more on:
http://stateofguns.com/heckler-kochs-hk-121/
Nifty.
But I didn't see anything talking about its performance after being caught in severe weather or in a harsh environment. Still cool.