How useful are ultrasonic cleaners in the gunshop? A current project is a 100-year old Parker SxS, the insides of which have a good century's worth of hardened gunk & dirt. Cleaning the inside of the frame and all those little parts by hand will be a big job. Any thoughts about how an ultrasonic cleaner would work in this application? Thanks.

I use one a lot. Really good for getting crud out of hidden areas, and combined with the heat, gets dried on gum/oil/gunk softened up. If you're working on 100 year old guns, it can clean them up a lot with less effort than hand cleaning.

What I have also seen done is take a sealed container, fill with solvent and immerse the parts in it, and then put that in the ultrasonic. Works better than the water, and forestalls any potential rusting due to the water. The ultrasonic energy goes through a plastic jar or bin wall. I haven't done this extensively myself, just a few parts in small bottles. It seemed to work better than the solvent alone would have.