Ok I know this has been done to death but a mate got me a lidl ultrasonic to play with. I thought at twenty quid it must be tat but after trying it today it impressed the hell out of me. Warm water. Little spot of fairy liquid and a squirt of lemon juice. Rinse brass after it in warm water. Very impressive result. No discolouring and shiney brass with even the primer hole clean.
Wonderment over now lol.