When I discovered dust cover was likely the cause of my 3 point jam feeding issue, I also had action opened by itself when firing. I could not finish a mag without a 3 point jam. Before it was a great shooter. I have/had 5 FALs/L1A1s and this one is the one I keep! When I came home, I remembered I replaced the dust cover with a new nice looking one just before. Checked the cover and it looked flush at the base, I took the cover off and hand cycle the action, every round chambered fine. I figured maybe the top edge caused the interference, ground it off a bit, took it back to the range and went thru 2 or 3 mags just fine. You can check if dust cover caused your problem by removing the cover and hand cycle with dummy rounds. If still jammed, cover likely not it, take a picture of the jam. There are many knowledgeable folks on this board can give you good suggestions.
As to your barrel time issue. Looks like under timed which means likely when they built the rifle they could not time any further. I had one Century like that, I bought it cheap then I knew why! I thought I could just time the barrel while I had the tools, wrong! It was totally stuck, I could not break the barrel with a 4 ft pipe on the barrel wrench and probably applied 200+ ft-lbs but it won't move. I applied heat, soaked with Kroil nothing worked. I gave up and used an end mill to deepen the sight adjustment screw hole to allow more adjustment, sold it a few years later. That was the only issue and I told the buyer, he was happy at the price while the sight off to one side is cosmetic.
Check the piston diameter also, unlikely cause, but check.
