Did you have issues when loaded to capacity? I just received a Lancer AWM 10rd in smoke and it was so tight to seat on a closed bolt that you had to forcefully jam it in. Then to release I had to use two thumbs with the receiver on a flat surface. I grinded down the follower stop by about 2 mm and now it seats/releases fine but it's easy to load 11 rounds. I also had to remove some metal from the two tabs because it would not drop free if I loaded anymore than 3 rounds. I've only put about 40 rounds through it so far (mostly suppressed) and haven't had any issues feeding or locking back.
OP, I sometimes carry my broken down 12.5" in a regular backpack. It's not as durable or purpose built like all the other $200 "discreet" rifle bags but no one bats an eye when I walk out the house with it. You can see the outline of the muzzle in the top left corner (not noticeable when slung) so I'd suggest something a little shorter in 5.56 or an 8-9" 300 BLK.