I promised I would provide feedback at some point, but my brain is slow and timid. My chief thoughts are as follows.
1. The arrangement of the bolt is one of the most peculiar aspects of the weapon. Your design certainly appears supported by sound technical reasoning regarding interplay with the rounds in the magazine. My concern is that a reduction in the number of bolt lugs will correspondingly degrade the precision of the weapon. Of course, this is in the context of military ammunition, and yet more worrisome, military shooters. Further, it is certainly reasonable to accept some loss of precision to gain increase reliability of the weapon during feeding, given your starting premise. I would, in short, like to see the data.
2. The retention of the AR-15 FCG components is an interesting move. I always thought it odd that fewer companies exploited reusing existing components in this fashion. If I'm understanding correctly, it would also be easy to move towards a "cassette" style of trigger pack, which is of growing popularity with the AR-15 market.
3. Your decision to devise your own magazine is admirable, and you certainly seem to have succeeded. My friend is curious if you can handle longer ogive, possibly ~66gr range EPR style 5.56 projectiles in the magazines. I'm not sold on drums, as their weight and bulk are disconcerting, but the ability to have them is never a bad thing.
4. I have no idea how you're going to solve the action-spring issue. I'm eager to see to what degree you can balance the forces acting on the bolt. Given you're trying to be unique, I wonder to what degree you'll end up matching the SCAR or other AR-18 descendants. Given the shape of the space you're working with, I do have my predicitions. (They mostly involve it being real goose hours, so I shan't share.)