I've fired Wolf through an HK 91 and an HK 45.
With the 91, it's great, and doesn't really seem *that* much more dirty than any of the surplus stuff I normally shoot. I prefer Barnaul to Wolf though, it seems to have more power behind the round, but that may just be my own misconception.
My friend has a WASR, and he only shoots Wolf 7.62x39, and loves it. My other friend has an AR-15, and he absolutely hates Wolf, and claims it jams the gun, and gunks up the bolt/receiver, and the cases melt, etc. So take what you will from that.
With the HK 45... it's really dirty. Instead of seeing the usual fireball exit the barrel when shooting, I see a huge black cloud exit the barrel, almost like in cartoons when someone falls down the chimney or something
The bullets seem to be more accurate than the WWB for some reason though...
The biggest problem is the primer has this red lacquer stuff which can melt and stick to the portion of the gun housing the firing pin, and it requires a little bit of elbow grease (as well as Break Free CLP) to clean.
Overall, I can't complain about Wolf ammo. As others have said, it's dirty, but it's cheap, and it lets you shoot more, which is always a good thing in my book. I always clean my guns almost immediately upon returning from the range though, I dunno if it'd be a bad idea to leave them lying around unclean having just shot a bunch of Wolf through them.