My previous assumption for failure-to-fire was, that the bolt didn’t close properly (possibly due to the overly tight extractor) and thus some of the power from the hammer was used to close the bolt and then there was not enough force to ignite the primer. Now it seems that the power from the hammer is lost somewhere else..
I previously noticed some wear on the recoil spring guide / bolt weight, but didn’t find what would have caused it or if it was there to start with, so I took a magic marker and painted it blue. Now it had new markings and some of them even pretty deep.
I had cleaned the rifle, done a little polishing and then of to range for test firing.
First 50 rnds (2 mags) seemed to be discharged without any problems, but then the problems started. Around 20% of the rounds failed to ignite on first try, but most ignited on second try, after being put back to magazine and re-cycled into the gun.
I collected some examples of fired casings and also some non-ignited rounds to check the firing pin markings. Then I also noticed that the first 50 rounds were not so successful and had included some bulged and deformed casings.
The plinker had a little facelift to enable better rifle-analogy in handling.
After the results of last magazine test, I ordered two Black Dog Machine 26rnd magazines and one 50rnd drum. Sometimes when filling up the drum, the rounds might get stuck on the corner of the feeding tower and the actual drum. (this might also be user related, one might even ask “what manual?”) Other than this, all mags seem to work flawlessly and time will tell if issues arise when they become dirty.