Hi 1K,
I saw your post a few days ago, and wanted to respond with a few photos, but Christmas kind of got in the way. I had the same experience with a Henry survival rifle (AR-7). The rifle wasn't feeding properly and shaving lead, so I chamfered the mouth of the chamber a bit. That solved the feeding problem, but then I started having a lot of misfires. I reshaped the firing pin, and recessed the pin slot to let it go farther forward. (In 20/20 hindsight, I don't recommend recessing the pin stop), I also bent the hammer spring to increase tension for a harder hit. The cases all had good dents in them, but I still had misfires. I finally faced the breech of the barrel, removing most of the chamfer, and that fixed the problem. Looking at the photo you posted, the chamfer on your chamber is pretty significant, much more than any .22 LR I have seen. When you consider where the priming mixture is on a .22 LR, you don't have much room to work with. If the head of the case under the priming mixture isn't directly supported by the chamber mouth, even a good hit doesn't seem to always ignite it. It's my guess that's your problem, you might call Ruger and have them take a look at the pistol.