Might be an issue with the gas system as you suspect, but seems to me that the result is short-stroking. Your 2nd and 4th pics are clues, and also that it happens more often with 8208 powder, which burns relatively fast. And 8208 causing short-stroking would be more prevalent in your rifle-length 19.5" versus your midlength 18", just as you're experiencing.
Not always a reliable gauge, but your ejection pattern could also be a clue. Further to the rear, around 4:30 or 5 o'clock, suggests weaker ejection versus spent cases going out at 3 o'clock. This could mean a gas system issue, or perhaps too much weight and resistance in the buffer system.
Instead of a heavier buffer, I suggest trying a lighter buffer, buffer spring, and / or BCG. If you don't have alternate parts onhand to test, cutting a couple of coils from a buffer spring might be the least expensive way to experiment.
Gas leak isn't uncommon, and yours might be excessive, but reducing the resistance in the setup might allow a little more rearward travel of the BCG when the weapon is fired. Factory 123's and 123 using 2520 will be more likely to work versus loads using 8208.
If it worked on AA's lower, the difference could be between your lower and theirs. If they're using a lighter buffer and / or spring, it would explain the difference in performance. Other variables between their results and yours might be ammo and magazines. And finally, if the system is right on the edge of reliable functioning, it will be more reliable without the added weight of a heavy optic and mount.
Try it without the scope and see what happens. Otherwise, lighten up on buffer and spring. And I wouldn't waste ammo using 8208 until you get reliability with slower powders like 2520 or factory loads.
Not always a reliable gauge, but your ejection pattern could also be a clue. Further to the rear, around 4:30 or 5 o'clock, suggests weaker ejection versus spent cases going out at 3 o'clock. This could mean a gas system issue, or perhaps too much weight and resistance in the buffer system.
Instead of a heavier buffer, I suggest trying a lighter buffer, buffer spring, and / or BCG. If you don't have alternate parts onhand to test, cutting a couple of coils from a buffer spring might be the least expensive way to experiment.
Gas leak isn't uncommon, and yours might be excessive, but reducing the resistance in the setup might allow a little more rearward travel of the BCG when the weapon is fired. Factory 123's and 123 using 2520 will be more likely to work versus loads using 8208.
If it worked on AA's lower, the difference could be between your lower and theirs. If they're using a lighter buffer and / or spring, it would explain the difference in performance. Other variables between their results and yours might be ammo and magazines. And finally, if the system is right on the edge of reliable functioning, it will be more reliable without the added weight of a heavy optic and mount.
Try it without the scope and see what happens. Otherwise, lighten up on buffer and spring. And I wouldn't waste ammo using 8208 until you get reliability with slower powders like 2520 or factory loads.
Drifter