Been tuning a Jennings .22. Yup a nice little beatup "ring of fire" zinc frame cheapo! When I got it, I couldn't even chamber a round. Excessive dry firing had beat a firing pin shaped dent above the chamber and the metal flowed into the chamber. A little filing fixed that. Then I polished the feed ramp until it fed better. Tweaked the lips on the mag to ensure proper feed as well. New firing pin and extractor springs. New recoil spring. This stupid little "junk gun" is ready to go! I haven't fired it yet, but am satisfied it it is ready to go. Found a lot of info on how to put these things in smooth order at
http://www.bryco-jennings-jimenezarms.com/forum/Yup, a junk guns fan forum! Woohoo! I'm hooked. There is something wonderful about taking a derided, POS that wouldn't work and making it into a functioning firearm again.
I'm not expecting thousands and thousands of rounds out of this. I'm going to put a few mag fulls through to satisfy myself as to it's function and my ability to hit things with it, then will keep it around as a small BUG...