Next to some other issues that I have with my Browning BL22 is that it very often misfires. And after a lot of thinking, trial and error, I think I have found the issue.
Remember the post about the little plate that came loose? The misfires are related to this as far as I have been able to figure out. There is a locking block that locks itself via this little plate. (I think i see wear on that block as well). Since it looks like the original plate is hand-made, I think somewhere in the process, someone did a very sloppy job.
OBSERVATION: The bolt is not sitting snug in its place when a cartridge is loaded. This cause the hammer to push through the play first and with the little energy that is remaining, the firing pin is being hit. This is causing the rimfire cartridge not being struck hard enough and thus causes a misfire.
The original plate is 20mm long, 10mm wide and 2mm thick.
I decided to print a few plates in two different lengths, 21 and 22mm. I know the prints are not exact, but this is close enough. 22 mm was way too long and the lever would not close. 21 mm was too long as well, so I decided to sand it down, little by little. If your lever does not FULLY close, do not force it shut and fire a live round! Your bolt may NOT be locked!

Eventually, with A LOT of assembling and disassembling, trial and error, I found out that the plate should be 20.15mm long. The size may vary per rifle, so keep that in mind.

I colored the piece of metal to make the scribe lines better visible, started measuring and scribing. I then used my desktop belt sander to gradually sand it so size. It is not hard to do but do wear gloves as the plate will be hot.
Look how nice the new plate fits snugly into its place. I temporarily glued it in place and went to the range to see how the rifle behaved.
The first 5 shots went without any problem. The next 5 produced 1 misfire and the next 5 were almost all misfires. What the heck happened??
Well, what happened is that I underestimated how much force is put onto the bolt and I had not harden the new plate.

Look at that dent! I did not expect that to happen, but this also points out to never underestimate the force that is put on the bolt.
So what to do now? Well, make an exact new one and harden it! The latter will have to be done later. Enjoy the photos and once I have hardened the plate and tested everything, I will post a follow-up.