I've run some less expensive lights on my shotgun before I knew any better. It isnt as bad on the AR though... Shotguns just have a lot more power. I've had everything from loose mounts to blown bulbs to parts falling off when using the shotgun. Im a big fan of the Surefire dedicated shotgun forends. I know its not the $50-$60 range, but they are relatively inexpensive when compared to a lot of their other lights (probaly around $200).

If you have a bayo lug on your 590, it will have to be shaved a little for the light to work though