You may be right about the extractor, either there or it caused the chunk ripped from the rim a t 6 o'clock? Hard to tell looking at just a fuzzy pic. Is the extractor in a FN-49 in the same orientation as in a FAL?
The only reason I mentioned premature unlocking is that there was an incident a while back with a FAL (as close as I can claim to expertise with an FN-49) where there was a slightly over-length gas piston fitted. There is meant to be a small (1/8" or so) gap between the piston rear face & the bolt carrier front face. this is designed (in a FAL) to create a short delay before contacting the bolt & carrier so that the breech pressure can drop lower before starting the unlocking camming. What that shooter was experiencing was very similar & it took a while to figure out as the difference was so slight it needed measuring to even find it.
Allan Quartermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”