Spend a little time perusing the internet. There are myriad accounts of people putting entire guns in an ultrasonic cleaner and screwing them up completely. Like this guy.
www.hkpro.com
Simon, I don't have an ultrasonic cleaner nor a desire to own one nor the time to search for it.
I do appreciate you posting the one example. I think the problem in that case might be the Simple Green cleaner, not the ultrasonic cleaner. If Simple Green is anything like like Super Clean, it has lye in it. I use lye-based products to strip decades-old enamel paint off of rare, valuable model cars so I can rebuild them. Lye eats old enamel without touching the fragile styrene plastic underneath, one of VERY few chemicals that will do so (most solvents that will take off enamel will also dissolve styrene). But lye also dissolves aluminum, and smells like rotten eggs as it does so. I found THIS out the hard way.
I have no idea what's in Simple Green, but I do know other modelers have used it to strip paint. Regardless of whether or not it has lye, it looks to me like it has SOMETHING in it that's reacting with SOMETHING in that particular gun or its finish. I can't conclude from that story that it's the ultrasonic cleaner that's the problem.
I'm not posting this to one-up you, I'm posting it just to pass along my personal experience with a couple of things. Others will have other experiences with other things; I invite them to share so we call ALL learn new stuff.
Oh, one other quick tip: #00000 steel wool and ScotchBrite pads are often used interchangeably in some hobbies. #00000 steel wool is a safe way to take surface rust off a blued gun, but try a ScotchBrite pad for than and you'll learn how FAST it will take off bluing.
I learned THIS the hard way, too.
