I have used mine to clean things other than brass. Everything I put in there came out very clean. Some things took more time than others though. I got one large enough to fit most of my handguns.
Getting one large enough to do a whole rifle could be pretty expensive. I think there are a few places in the DFW area that offer this as a service.
If you are looking to buy one, grizzly has some larger models, but I’m not sure any of them would fit a whole rifle.
I’ve also seen some discoloration of plastic parts when using some of the stronger cleaning additives. For some reason I thought it would do a good job of cleaning my eyeglasses; it removed the paint from the frame, lenses came out fine.
http://www.grizzly.com/search?q=(categoryid:150220) http://www.grizzly.com/search?q=(categoryid:778720)