Lil'gun actually does well for subs and is one of the powders I've had success with. IMR4227 is the powder I've worked with most developing my sub loads though because lil'gun and 1680 was unavailable for so long I had no choice. 296/H110 need to be relegated to supersonic only. Also you need to switch from your CCI400 primers the the magnum CCI450 primers; it makes a difference. I would also suggest you switch to an H-2 or ST-3 buffer. It will increase bolt dwell time and improve cycling. If needed I can go back into my research and show you where it is recommended by AAC in their data sheets.
I'm at work now and don't have access to my load data but I can tell you the buffer and the proper primers brought it all together for me when I was going through what you are now.
Actually I was able to find to AAC reference document here: http://www.advanced-armament.com/assets/images/pdf/manuals/300BLK-AACUpper-MiniBro.pdf
Let me know if there is anything I can do.