Gen 3 cycling issues

BRN-180 G3 300BLK 9”, BCM lower, SiCo Hybrid 45 can. Gun is locking bolt to the rear as if mag is empty when there’s still ammo loaded. Happens with supers, FMJ, and subs on the correct gas setting. Ejection pattern looks good for each respective round on the correct setting (2-4 o’clock). Tried swapped lowers but issue followed. Can’t think of why this is happening, has anyone experienced this issue or could clue in on why this would occur?