A superb, reliable, accurate weapon system. Why the British Army didn't buy this system instead of the SA-80 escapes me (especially considering they had to go to H&K in order to make the improvements for the A2!).
A very gucci family of weapons but not entirely fault free. Cleaning them can be a pain in the arse and the HK53 (aka The Assault Rifle of the Gods and "Something For the Car Bag, Boss?") has a tendency to fail to eject spent cases which then get mangled and jammed inside. Oh yes, and many users of the MP5K discover, after moments of high excitement, that they've shot the end of their left hand index finger off, which can be a tadge irritating. Still, overall a very high quality system which does what it says on the tin (Heckles and Coughs?).
Something not reccomended to do with an HK G3K, a short version of the 7.62mm G3, is to fire it on automatic from the back seat of a car through the windscreen when the windows are shut, after about 5rds everybody's ears bleed, the driver and front passenger's hair smoulders, the empty cases bounce off the side window and go down your shirt and the concussion makes your eyes water. So I've been told.
That last paragraph is precisely on the money, but omits the telling detail that, when doing as it is suggested was done, the muzzle climbs under the impetus of fully-automatic fire and the windscreen, headlining and, if very fortunate, the roof, all get perforated. Another amusing side-effect of this sort of activity, hypothetically, is that if the vehicle should be moving at greater than, oh, 20 mph or so, both front-seat occupants acquire a lap full of granules of windscreen glass. This tends to add to the stress and confusion of the situation which led to the hypothetical release of 7.62x51 from the back seat.