Ultrasonic Cleaners
One caveat regarding the use of commercial ultrasonic cleaners is their frequency rate and power.
Those designed for firearms are generally safe for night sights but a commercial unit is not. Get a letter from the manufacturer stating that their cleaning unit is safe with the materials you intend to clean.
I clean all my firearms, steel, aluminum, polymer, with an L&R ultrasonic cleaner using their solvent and have never had a problem. They also make a cleaner for cleaning handcuffs used in detention facilities and another cleaner for other medical uses. These cleaners are not the same as the one they supply for firearms.
I simply field strip the firearm and put it in the stainless steel basket supplied and run the cleaner solution/water displacement solution for ten minutes for each cycle.
Ultrasonic cleaning will not remove the lead fouling but it loosens it's bond with the metal and a jag and patch will push an amazing amount of lead granules out of the bore.
A note of caution. The oil bath is not a lubricating bath but a water displacement oil bath. After taking the gun out and letting it dry properly lubricate the gun IAW it's manufacturer's specifications.
Not having ever done it I can't tell you that if you don't lubricate after the oil bath that the gun will rust rapidly.
Also not having done it I can't tell you that trying to use the water displacement oil bath past it's service life leads to the water not being displaced and the gun rusting even more rapidly.