What cleaners are you all using?

So I have an AR in the shop that is completely covered in carbon build up and even after a soak in hot water and cleaner it looks like I'm going to have to scrap it off. A buddy recommended MPro 7 to clean it but it leaves a film and doesn't really work. so my question to you all is

which cleaner is everyone using for heavy carbon build up?

what works best in an ultrasonic for parts cleaning?