Since no where in your post did you say it has to be 5.56, if you want to go short sup 10 inch then I would suggest at .300 black out. with that you can get as short as 7.5 running reliably though 9 inch is the best. It will give you something compact to work in and around a vehicle or home and with a law folder can be thrown in a back pack. As for PSA they can be hit or miss on things but they always make things right, they just aren't good with communication, granted this from my one and only interaction with PSA. But if you get a lower drop and upper on it to make sure it is in spec, mine was out of spec when I got it among other things. As for and upper if you want fully build grab a BCM 9 inch, Areo 10.5, SLOGW East India or whoever tickles your fancy. Throw your dot of choice and light and sling and call it done.