I myself had experienced the same problem.
Gunz one day can be fine hours on end and then other days it'll be an hour on playing then I'm faced with 'Gunz is not responding' ...
I play on a laptop btw, now what I found that was causing this reoccurring problem was due to my laptops memory modules failing caused by overheating. Once the modules were replaced the problem stopped being as persistent, though time to time I find it still happens which I put down to temperature problems as it only rarely does after long hours playing.
I'm not saying this is the problem you are having but it could be a possibility, try monitoring your temperatures from start up to the point of when you receive the problem of crashing.
Clean your fans and vents.
Try a cooling pad if you're using a laptop.
Close back ground processes that are running that aren't necessary.
Google - Laptop cooling / Desktop cooling for more tips.
