The HK G36 is a 5.56 mm assault rifle, currently in use with, amongst others, the German and Spanish military. It's noted for accuracy and reliability, although some users report that it does not seem sturdy enough. For more info have a look here:

though as with all Wikipedia entries take things with a pinch of salt.

This thread got me thinking (I may be wandering off topic here), there are a lot of Doctor Who stories that could be played out using WWG. The obvious examples are the sci-fi sets. First Light could easily represent an Earth ship raided by the Ogrons in 'Frontier in Space'. Mars Station and Platform Command could be used for Sanctuary Base 9 from 'The Impossible Planet/The Satan Pit'.
But then again, there are many stories that featured old mansion houses. 'The Evil Of The Daleks', 'Day Of The Daleks', 'The Seeds of Doom', and 'Ghost Light' are the most obvious. Hello, Shellendrak Manor!
The City of Mayhem is ideal for all those alien invasion stories (especially when Underground comes out. Perfect for Yeti!). Castles have often featured in the historically based episodes. And CaveWorks looks like it could stand in for any planet that even remotely resembles a disused quarry!